I would like to ask if anyone knows what word-formation process takes place when we join two separate words (for instance 360 + flip) and create a word '360 flip' written separately, but used as a single noun (He did a beautiful 360 flip trick). I know that compounding means the joining of two separate words to produce a single form, but this is different because in my example we do not have one single form.
As far as I know, compound nouns can be spelled as one word (toothpaste), two words (vacuum cleaner) or with a hyphen (radio-controlled). Often there is more than one option. Therefore your example is in my opinion also a compound noun.
Someone had to compose an answer, so I'll just give myself the honours. As all the commentators have said before, it is indeed compounding, spelling has nothing to do with it being treated as one lexical item. But if you pronounce it three sixty flip, that is also a shortening of three-hundred-sixty degrees flip.