Literally translated: "or something like that"
A phrase said after a vague or exaggerated example.
Usually used when talking about someone or something in the third person.
"James and Gregg are always running off together. They are probably gay for each other or some shit."
"This bus seat is wet, the guy before me must have pissed here or some shit."
Person 1: I saw this interview of Quentin Tarantino yesterday.
Person 2: Who the hell is Quentin Tarantino?
Person 1: That guy that directed Pulp Fiction or some shit.
When something or someone has "seen some shit", it vaguely means that something or someone might have gone through trouble in the past, in which said experience could result in wisdom.
I got my bike used. It was cheap but it's probably seen some shit.