I think "repertoire" is basically all the pieces/songs you can more-or-less perform. Out of those, for given musical projects, bands, events, etc., you establish a selective repertoire geared towards that purpose. That can vary depending on who your audience will be and how you want them to react to your music, or what you want them to experience, or how to perceive you. It is tailored to each instance, or to your general project. One typical consideration, for example, is in creating a "balanced" set of music for performance X. A lot of chantey singers, for instance (though I am not a big fan) will make sure they have "John Kanaka" in their repetoire because they will often find themselves in the situation where they want to portray the image of a "diverse" influence on chanteys. Another example is the decision whether to have mostly original songs or mostly "traditional" songs, the balance of which will greatly shape how an audience receives your music.

Gibb