The original bottle cap was called Crown cork. It is pressed onto the bottle, and can be removed, using a bottle opener.
In recent years bottle caps with screw on mounts are used that way, a bottle opener is no longer required. Caps for plastic bottles are often made of a different type of plastic from the bottle.
A cork is another type of closure for the top of a bottle.
Other websites[change | change source]
Media related to Bottle caps at Wikimedia Commons