Stranger: Someone I have never met or talked to at all.
Half Stranger: Someone who I see often, but never have to talked, for example, this lady who takes the same bus as me at the same time, I never talked to her, she has never talked to me, but I know who she is.
Half: Acquaintance: Someone who I don't see often at all, but I would know them if I saw them and they would know me if they saw me.
Acquaintance: Someone who I see often and talk to, but never talk about anything serious with. I may just say "hi" to them or ask them how they are.
In-Betweener: Someone I talk about school/work-related stuff with, but don't talk about general life stuff very often. Like a science partner for example. I probably wouldn't feel comfortable doing something outside of school/work with one of these people. Non-school/work may fit into this category as well in some cases, which would mean someone who I know better than an acquaintance, but not as well as a casual friend.
Casual Friend: Someone I talk to about non-school/work related stuff with, but probably won't wouldn't go to for emotional support. I may or not do things outside of school/work, but I'd feel comfortable doing it.
Close Friend: Someone I'd go to for emotional support. I mostly likely to things outside of school with this person.
There are also people who I don't like that fit into totally different categories than these.