The question is motivated by this post in the Russian forum, where the answers repeatedly refer to verb пересечёмся as "young people's slang" or "teenage slang". (пересечёмся = "we'll cross each other" in the sense "we will meet".) This made me think that, first of all, the young people/teenagers in question were young in 60s-70s, whereas by now there are several generations of Russians who use this expression. Moreover, I would not call it slang, as this implies pejorative meaning and the use in specific social groups, whereas the expression is in broad use use today. Still, it certainly belongs to colloquial/informal speech.
The question is about the difference between slang, jargon, colloquial and informal or, more formally, about the classification of various colloquial uses. I think it belongs to the area of sociolinguistics, which is why I post it here. However Foreign languages forum might be also an appropriate place.
Here is a related question, although mine seems broader in its scope.