Completely clueless about sergers Sewing Machines Parts and Sales in Los Angeles

So I'm getting a serger for my birthday and so I'm starting to research what I want… But I have no idea what I'm looking at. I've been sewing for LOTS of years and never once used a serger. I want something that can do hems and the like, but I'm just clueless as to what makes the $650 Janome better than the $250 Singer when they look like the same machine. Or even a $100 off brand for that matter. And also lost on the jargon, what's an overlock etc.?