Stems can refer to two things in music, relating to music notation and production.

Notation

Stems are the lines which extend from the notehead. Stems may point up or down. Different-facing stems indicate the voice for polyphonic music written on the same staff

Staff (music)

In standard Western musical notation, the staff, or stave, is a set of five horizontal lines and four spaces that each represent a different musical pitch—or, in the case of a percussion staff, different percussion instruments. Appropriate music symbols, depending upon the intended effect,...

. For single-note melodies, the stems usually point down for notes on the middle line or higher, and up for those below. If the stem points up from a notehead, the stem originates from the right-hand side of the note, but if it points down, it originates from the left. The exception to this rule is when a chord contains a second, in which case the stem runs between the two notes, the higher being placed on the right of the stem and the lower on the left. The length of a stem is usually that of an octave on the staff, going to either an octave higher or lower than the notehead, depending on which way the stem is pointing.

Production

Stems are the individual components of a mix

Audio mixing (recorded music)

In audio recording, audio mixing is the process by which multiple recorded sounds are combined into one or more channels, most commonly two-channel stereo. In the process, the source signals' level, frequency content, dynamics, and panoramic position are manipulated and effects such as reverb may...

, separately saved (usually to disc) for the purposes of use in a remix

Remix

A remix is an alternative version of a recorded song, made from an original version. This term is also used for any alterations of media other than song ....

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