Uh-oh, are we talking about nomenclature in compositional form? One of my favorite topics! 😈
Seems like OP's question has already been sorted, but just to pile on, yes, a "soli" is a particular "show off the ensemble" section of an arrangement, usually in a jazz big band, while an "interlude" can really be anything that diverges from central themes within a larger work.
Generally, theoretical terms like these should be practical and aid with communication, not add to confusion. There are just so many that have accumulated over the centuries that they often do the latter. Music is deeply tied to society and culture, which are not elegantly designed things, so there's a ton of terminology that evolves organically and sloppily within any tradition. And it can be different from region to region, even within a relatively codified scene.
Don't get me started about you Englishmen and your quavers.