Suspended (sus) chords: Chords which replace the third with either the perfect fourth or the major second. Because these chords do not play the third in the scale, they are neither truly major nor minor.
Ninth chords: A ninth chord, for example C9, is formed using the major triad, plus the seventh and ninth scale degree. When called a “dominant ninth” or when not otherwise specified, the chord uses a minor seventh. If the chord is called major (Cmaj9), then the major seventh is used. In both cases, the ninth is an octave above the major second, not the minor second.
Impromptu: In both musical performance and general usage, impromptu means, without pre-planning. For example, a band taking requests from the audience is creating an impromptu setlist.
Improvisation: Creating music (or anything else, really) “on the fly”. For example, a Jam band might improvise additional sections to their existing songs.
Enharmonic: Notes that map to the same pitch are considered enharmonic. For example, C♯ and D♭.
Fermata: A fermata is a musical notation symbol placed over a note or rest to indicate that the note or rest should be held longer than its typical duration. The exact length of the hold is left to the discretion of the performers and/or conductor, however most often the length is doubled or more. Although less common, an inverted fermata can be used under a note or rest. The effect is the same. Due to its appearance, the fermata is also sometimes called the “birdseye” or “cyclops eye”. Due to its effect, it is also called a “hold”, “pause”, or “grand pause”. For more information and a visual example, see the Wikipedia entry.
Bus: In audio mixing, a bus is any path through the mixer that allows for adding multiple audio signals together, processing them as a group, and directing them on to another bus or to an output channel.
Channel: In audio mixing, a channel is an input or output to get audio signals into or out of the mixer. Most mixers allow each channel to have its own processing (e.g. equalizer, FX, volume fader, and pan). Mixing hardware is often sold by the number of channels available. A 32-channel mixer, will have 32 input channels. A 4/2 desktop mixer will have 4 input channels and 2 output channels.