A production can be divided into stems such as vocals, drums or other instrument groups. Keeping these parts separate lets an editor adjust, combine or process them without making the same change to the entire mix.
A stem is not necessarily an individual original recording track. Its contents and separation quality depend on how it was exported or extracted, and access to stems does not itself establish reuse rights.
ELI5
Think of a song split into separate sound layers that can be adjusted individually.
For example, a vocal stem can let an editor lower the singing while keeping the instrumental parts at their existing level.
Is a stem always one instrument?
No. It can contain one component or a group of tracks, depending on how the mix was organized and exported.
Does downloading stems grant every reuse permission?
No. The technical file and the rights to reuse its contents are separate questions.
