Music-styles

I listen to music very much, but something I don't really understand are the different styles/genres. I've heard these names very often and probably I know all the styles/genres, but can anyone explain to me what the 'definition' is of the following styles/genres including some (popular) bands who are representating these genres:

Emo-core
Hard-core
Post-hardcore
Grind-core
Punk
Powerpop
Indie(core)

It's just for me to know some definitions, it's not that I stick genres to bands or something.
 
Emo-core - Emo mixed with Hardcore. Glassjaw is probably the best example, as are Blood Brothers (despite the fact that they suck, they show what the genre is).
Hard-core - Black Flag was one of the first bands and probably most easily recognized. Essentially Punk but heavier, usually with screams for vocals.
Post-hardcore - Poison the Well type stuff. Pretty much hardcore but more progressive and based in newer music.
Grind-core - Death Metal mixed with Hardcore. Napalm Death is probably the most well known Grindcore band.
Punk - Ramones, Sex Pistols, etc. Fast, simple rock 'n' roll, basically.
Powerpop - Basically just standard rock with many hooks. Weezer is the most popular currently.
Indie(core) - Don't know about 'core', but as far as Indie goes, Pavement, Built To Spill and Yo La Tengo are some of the better bands in the genre. 60's based rock, usually with influences of Velvet Underground and other psychadelic bands.

I'm not sure if all of these are current, I'm just saying as much as I know.