Everything is practice

Okay, that's not really true. Not practicing is definitely not practice. I think what I really mean is something more like "everything you do that involves learning about your instrument, and music in general, is practice".

Playing your instrument is practice (obviously).

Learning theory counts as practice.

Listening to music can be practice if doing so teaches you something new about your instrument (or something like songwriting, for example).

Tapping rhythms on your leg while waiting for an appointment somewhere is rhythm practice (although it might drive others a bit crazy!)

Imagining yourself playing is practice.

I've talked before about how there's really no excuse not to practice, and I think this short list (which could easily be expanded) is proof of that. 

Practice creatively, have fun, and practice often!