In early versions of Foldit, freezes were referred to as locks. Some pages on this wiki still use "lock" to refer to a freeze.
Unlike a freeze, there's generally not a clear visual indication when segments are locked. Recipes can detect locked segments using structure.IsLocked. Certain color options, such as EnzDes, may show locked segments in a darker color than unlocked segments.
With freezes, recipes can use freeze.IsFrozen, which returns separate indicators for the backbone and the sidechain. With locks, there's only a single 'locked' indicator.
Locked segments may or may not have zero segment score. In some cases, a locked segment with a non-zero score may have an unlocked sidechain. The sidechain can potentially be moved to different positions, affecting the segment's score.