Samplers do not agree on what to call anything. An MPC keygroup, an Ableton multisample and a Kontakt instrument are the same object under three names, and that mismatch is most of what makes sampler documentation hard to read. This lines the words up.
Keygroup
MPC. Elsewhere: zone, region, key zone
A keygroup is one slot in an MPC program: a root note, the range of keys it answers to and the samples it plays. Build a keygroup for every note you sampled and you have a playable instrument.
The word is MPC's. Kontakt calls the same thing a zone, SFZ calls it a region and Logic calls it a zone as well. On r/MPCUsers the vocabulary is decisive: producers there say keygroup and almost never say multisample.
Multisample
Ableton, hardware samplers. Elsewhere: instrument, library, keygroup program
A multisample is a set of recordings of the same source captured at different pitches, and often at different volumes, mapped so the sampler picks the closest one for whatever note you play.
The point is that one recording stretched across two octaves stops sounding like the instrument. Capturing every few semitones keeps the character intact. One word, no hyphen.
Chromatic mapping
Also: pitch mapping, key mapping
Chromatic mapping is laying samples across the keyboard so each one plays at its recorded pitch on its own key, and the notes in between are filled by pitching the nearest neighbor up or down.
It's what turns a folder of files named by note into something you can play. The mapping is only as good as the note detection behind it, which is why a folder with no note names in the filenames defeats most tools.
Velocity layer
Also: velocity split, dynamic layer
A velocity layer is a second recording of the same note played harder or softer, triggered by how hard you hit the key. Three layers on a piano note means three genuinely different performances rather than one recording turned up.
Layers cost memory and they cost recording time, so formats cap them. An MPC keygroup holds four. Anything mapped deeper than the target format allows gets thinned out on export.
Round robin
Also: alternation, RR
Round robin cycles through several recordings of the same note at the same velocity, so repeated hits are not identical. It's the standard fix for the machine gun effect on drums.
It's a different axis from velocity. Velocity layers change with how hard you play, round robins change because you played again.
Root note
SFZ: pitch_keycenter. Elsewhere: base note, original pitch
The root note is the pitch a sample was actually recorded at. The sampler needs it to know how far to shift the audio for every other key in the range.
Get it wrong by a semitone and the whole zone is out of tune with the rest of the instrument, which is the usual explanation for a mapping that sounds fine alone and wrong in a chord.
Key range
SFZ: lokey and hikey. MPC: low note and high note
The key range is the span of notes one sample answers to, usually written as a low and a high note either side of its root. A sample recorded at C4 covering B3 to C#4 is doing one semitone of stretching in each direction.
Wider ranges mean fewer samples and more artificial pitch shifting. How wide is too wide depends entirely on the source: a pad tolerates a fifth, a snare barely tolerates a tone.
One shot
Also: single hit, hit
A one shot is a sample that plays to its end and stops, with no loop and no sustain. Kicks, snares and stabs are one shots.
The distinction matters at export time. A one shot needs no loop points, while a sustaining instrument sample is unplayable without them because holding a key past the end of the recording produces silence.
Loop point
Also: sustain loop, loop markers
Loop points mark a section in the middle of a sample that repeats for as long as you hold the note. They are what let a two second recording sustain indefinitely.
A good loop lands on matching waveform positions at both ends. A bad one produces an audible click once per cycle, which is the sound of the waveform jumping rather than continuing.
Loop crossfade
SFZ: loop_crossfade
A loop crossfade blends the end of the loop back into its start over a short overlap, so the seam is smoothed rather than cut. It's the standard rescue for material that will not loop cleanly, such as anything with vibrato or noise in it.
Formats disagree on units. SFZ expresses the crossfade in seconds while other formats count samples, so the same number does not mean the same thing once the sample rate changes.
Program, preset, instrument
MPC: program. Decent Sampler: preset. Logic and Kontakt: instrument
All three words name the same object: the file that describes how a set of samples is mapped, without containing the audio itself. Which word you use is a matter of which machine you learned on.
The vendor convention worth knowing is that a multisample is the input, a folder of recordings, and the instrument is the output, the thing you can play. Sample Miner follows that convention.
Keygroup program
MPC. File extension: .xpm
A keygroup program is the MPC's complete instrument: every keygroup, its samples and its filter and envelope settings, saved as an .xpm file.
It's the MPC's name for what Ableton would call a multisample and Kontakt would call an instrument. The samples sit beside the .xpm in the same folder rather than inside it.