Hello. I'm now studying transistor amplifier circuit and I have some confusion of definition of amplifier classification. I thought common emitter means emitter side is grounded, although there is actually some elements between emitter and ground in practice. So I thought "common" means "grounded". But when I looked at other configuration like common collector (See http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/npncc.html#c1) it seems collector side is not grounded side. How is each configuration defined? How does each configuration differ from the other?