Of these two nouns, repertoire is much more general, while repertory has a related, narrower meaning. The origin of these words, Latin re-parare, means to “re-produce” (to produce again), and both words concern creative works that can be performed again and again. Let’s look at each word in more detail.
Repertoire means “a collection of works in the performing arts (in music, drama, dance, etc.) known by a particular performer (person or group), or created by a particular composer, or thought of as a collection for other reasons, such as genre.” Most often, it has the first meaning—all the works known by a particular performing artist or group:
My repertoire of gypsy jazz songs is very small; I only know a few songs.
But repertoire can be used, metaphorically, for all kinds of things:
That politician has a huge repertoire of lies. (repeated lies)
Chili dogs are not in Sally’s repertoire. (repertoire of foods she can prepare)
Any action that can be imagined as a repeated performance can belong to a repertoire.
Repertory is also a noun, but often used like an adjective, as in the terms repertory theater and repertory company—a theater, or theatrical company that performs a collection of different works each season:
Victoria joined a repertory after college to get acting experience.
Repertory can also mean “repertoire” or “repository” (a place where things of any type are collected), but it usually means “repertory theater.”