You've been given excellent answers on this question. I would like to add that in my region "later" is VERY informal and considered slang...as in "later dude". I never use "later" unless I am just being silly with friends. I use "see you later" all the time with people I know..my friends, my boss,...basically everyone. I typically use "goodbye" when on the phone with someone I don't know. "Bye" is fine to use as but it is less formal than "goodbye". Here's my breakdown: 1. "goodbye" is the most formal 2. "See you later" = "Bye" (these are equal in that they work in the same situations) 3. "later" - least formal (Personally, I would not use...depends on the region I guess)