The Region Menu is where the user can tweak its regions, the parts of audio or MIDI that sit on the timeline.

Insert Region from Source ListIf a region is selected in the Editor List, add it at the Edit point
Play Selected RegionsStarts playback at the beginning of the selected region(s), and stops at its(their) end
Tag Selected RegionsPrompts for a text to tag all the selected regions, this tag is visible in the Region list
LoopCreates a loop range on the selected region's boundaries, and starts the looped playback
Rename…Changes the name of the region, that appears in its top left area
Properties…Shows the Region properties window, that displays detailed information about the region and allow for some modifications
Loudness Analysis…Shows the Audio Report/Analysis window, that displays detailed dBFS information as well as a spectrogram (dBFS of frequency against time)
Spectral Analysis…Shows the Audio Report/Analysis window, that displays a integrated spectral view of the region (dBFS against frequency)
Edit
CombineCreates a new region by joining the selected audio regions in the same track, and replaces those region with the newly created compound. The same rules are applied to create the compound as for playback regarding e.g. layering
UncombineSplits back the compound created by combining into its original audio regions
Pitch Shift…Changes the tune of the audio region, by octave, semitones or percentage, based on spectral analysis. Optionally, and if they have been set for the region, preserves the formants
Split at Percussion OnsetAllows splitting the selected regions on its Percussion Onsets marker as set by the Rhythm Ferret (Not usable as of 5.5)
Make Mono RegionsCreates mono regions out of a stereo or multichannel region by splitting it into its discrete channels. The created regions are added to the Editor List
Close GapsExtends (or reduces) the selected regions to be perfectly aligned. Optionally, sets up a crossfade duration, or a pull-back (spacing between regions)
Place TransientPlaces a transient at the Edit Point. Used e.g. for the Pitch Shift… action
Rhythm Ferret…Opens the Rhythm Ferret which is a powerful tool to sequence audio files
Strip Silence…Opens the Strip Silence window which is a very handy tool to remove all audio under a user-chosen threshold (with a preview)
ReverseMirrors the audio horizontally
Layering
Raise to TopOn overlapping regions, puts the selected one(s) on top
RaiseOn overlapping region, makes the selected one(s) one layer higher
LowerMakes the selected region(s) one layer lower
Lower to BottomSends the selected region to the background
MIDI
Transpose…On a MIDI region, shows the Transpose MIDI window, allowing to shift the pitch of the whole MIDI region by ± n semitones or octaves
Insert Patch Change…Inserts a patch change at the Edit Point, allowing a change of patch, channel, program and/or bank
Quantize…Shows the Quantize window, allowing to perfectly align the MIDI notes to the musical grid
LegatizeShortens or elongates the MIDI notes to make them perfectly sequential, i.e. the end of a note is the start of the following one
Remove OverlapShortens or elongates the MIDI notes to make them perfectly sequential, i.e. the end of a note is the start of the following one
Transform…Transform window, that allows for mathematical operations on the midi notes
Unlink all selected regionsMakes the selected MIDI regions independent, e.g. editing this region won't affect any other one.
Unlink from unselectedMakes the selected MIDI regions independent from regions outside the selection, but keep the link between the selected ones.
Deinterlace Into LayersSplits the selected region(s) to create in-place copies each containing only one channel. A region containing e.g. 3 channels will generate 3 stacked regions containing 1 channel each.
List Editor…Shows the List Editor which sequentially lists all the MIDI events in the region, and allows for precise modifications
Gain
□ OpaqueWhen checked, makes the region opaque audio-wise, i.e., the underlying regions won't be audible
□ MuteWhen checked, mutes only the selected region on the track, without muting the track. The muted regions will have !! prepended to their name and will be semi-transparent
Normalize…Shows the Normalize region dialog, which allows to scale the region level by setting its maximum level, optionally constraining the RMS
Boost GainIncreases the gain on the selected region by boosting the audio, without touching the envelope or automation
Cut GainReduces the gain without touching the envelope or automation
Reset GainIf the gain has been edited, revert to its initial value
Reset EnvelopeIf the gain envelope has been edited, resets it to its initial value (constant at 0 dB)
□ Invert PolarityWhen checked, inverts the signal's phase in the selected regions and renders the symbol (a diagonal line across zero) next to the names of affected regions
□ Envelope ActiveWhen unchecked, disables any envelope editing that has been made. The envelope will be displayed in yellow instead of green.
Position
Move to Original PositionMoves the region where it was initially recorded or inserted in the session
Snap Position to GridIf the Grid Mode is set to Grid, snaps the region to the nearest grid line
□ LockLocks the selected regions at their current positions in time and tracks, avoiding any movement on the timeline. The region name will be surrounded by > and < brackets
□ Glue to Bars and BeatsLocks the region position to relative to the musical grid, i.e. a change of tempo will move the region to keep it on the same bar/beat
□ Lock to VideoSame as above, relative to the position in the video
Set Sync PositionCreates or move the Sync position, i.e. the point of the region that will be aligned or snapped to the grid, and that is (by default) the beginning of the region.
Remove SyncRemoves any user defined Sync point, and resets the sync position to the beginning of the region
Nudge LaterMoves the region to the right by the amount shown in the nudge timer
Nudge EarlierSame as above, to the left
Nudge Later by Capture OffsetMoves the region to the right by the capture latency computed by Ardour based on the user's settings regarding latency
Nudge Earlier by Capture OffsetSame as above, to the left
Sequence RegionsPuts the selected regions one after the other, so that the end of one region is the beginning of the next one, removing any overlap or silence. The reference point is the earliest region.
Markers
Add Region Cue MarkerOpens a dialog to enter a region-level marker at the mouse pointer position
Clear Region Cue MarkersRemoves all markers from the selected regions
Convert Region Cue Markers to CD MarkersConverts all markers from selected regions to CD markers, bit doesn't delete original region-level markers
Convert Region Cue Markers to Location MarkersConverts all markers from selected regions to location markers, bit doesn't delete original region-level markers
Trim
Trim Start at Edit PointIf the Edit Point is within the region boundaries, shortens the region to align its start with the Edit Point
Trim End at Edit PointSame as above, for the end of the region
Trim to LoopUses both the start and end Loop markers to shorten the region
Trim to PunchSame as above with the Punch markers
Trim to PreviousOn overlapping regions, shortens the selected one so that the previous region is complete, i.e. the new start point for the selected region is the end point of the previous region on the timeline
Trim to NextSame as above, with the end of the selected region aligned to the start of the following one.
Ranges
Set Loop RangeCreates a Loop range based on the selected regions, i.e. the start of the loop range is the start of the earliest region, and the end of the loop is the end of the latest region.
Set PunchSame as above, for the Punch range
Add Single Range MarkerSame as above, for the Edit range
Add Range Marker Per RegionFor each selected region, creates its own Edit range based on the boundaries of each region
Set Range SelectionCreates a range selection based on the boundaries of the selected regions
Fades
□ Fade InActivates/deactivates the Fade In at the start of the region
□ Fade OutSame as above, for the Fade out at the end of the region
□ FadesShortcut to activate/deactivate both the fade in and fade out
Duplicate
DuplicateCreates a copy of the selected region(s) and appends it to the original
Multi-Duplicate…Shows the Duplicate dialog, allowing to create multiple copies, or a not-integer number of copies (the last one will then be truncated)
Fill TrackCreates duplicates until it fills the session, i.e. reaches the End marker of the session. The last duplicate may be truncated to fit in
Export…Shows the Export dialog, with all parameters set to export only the selected region(s)
Bounce (without processing)Creates a bounce, i.e. a version of the region with all the edits (boundaries, envelope), as a new region in the Editor List, without any of the effects of the mixer strip
Bounce (with processing)Same as above, with the effects of the mixer strip
RemoveDeletes the region from the edit (no file is harmed in the process, and the region stays in the Editor for later use)