I suggest NOT getting too tied up in specific terminology for things that are really "non specific" - since virtually anything NOT a "solo" is a "backup part".
You can kind of stuff anything "out front" as a "solo" - intros, outros whatever - again, terminology just isn't that important. You can NOT call some of them solos if you want.
And "parts" played as "backup" are going to be parts of solos at other times...and visa versa.
It all overlaps and is interchangeable. If you "categorize" certain things you play as only "backup" or "solo" parts your playing is likely to sound very stiff and "manufactured".
This can also be a problem if you only work on playing things exactly as found in tab. Try varying things, mixing them up, changing keys etc. It will help you improvise, and virtually save your behind if you ever get lost for even a few notes when playing with others. Even being able to play a few simple notes in the right key when lost can make you a far better player.
In short - try not to get locked into precise terms and always playing exactly the same thing. It's not as hard as it sounds and even loosening up your terminology will help your playing. Mostly - have fun. If you're stressed about anything it'll be "heard". _________________ No chops, but great tone