DING DING DING SOUND THE ALARM!...

Stupid question again....why do the specify "hydraulic" on all the heads?
I didnt realize there was a difference in heads between solid and hydraulic??
I think one is actually for roller lifters with stronger Springs and one is not. But the other products are decent quality these days and cheap there right up still lack quite a bit. Do they still say they have a 2.202 intake valve?..