A lock token is a unique token associated with a lock/unlock pair (or tuple), as determined by lock pairing. Typically, a lock token consists of the object pointer to the Java monitor object with a few extra bits of information at the least significant byte, keeping track of how this monitor is currently locked. Examples of information that is stored can be "thin locked", "fat locked", or "locked recursively". The lock token can also flag the lock or unlock instruction as "unmatched" if it isn't possible to determine where the other half of the lock/unlock tuple is. This is unusual but possible, due to the nature of Java bytecode, and makes for slower synchronization than with paired lock tokens.
See also Lock pairing.