or what are effects loop?

aps with these seems to be better than amps without these, but i dunno what it is.
anyone would like to teach me?

btw is there any sticky here with info about differences between active and pasive pups? i haven't found any...
Quote by FatalGear41
When you break a bass string, that snapping sound is the sound of six dollars going down the crapper.

Sterling Ray 35
Hartke Ha3500 head - Gallien Krueger 212MBE cab
Tech 21 VT Bass
Zoom b2