Cam, Friend, SLCD
Cams, also known as friends, or SLCDs, are spring-loaded devices used for protection in cracks. Cams are considered one of the safest means of protecting a crack, but they are also the most difficult to learn to place.
The Climbing Glossary - Cam, Friend, SLCD

Cam, Friend, SLCD
Cams, also known as friends, or SLCDs, are spring-loaded devices used for protection in cracks. Cams are considered one of the safest means of protecting a crack, but they are also the most difficult to learn to place.