Bound threads are created PTHREAD_SCOPE_SYSTEM. A boundthread is permanently attached to an LWP.
Each bound thread is bound to an LWP for the lifetime of the thread. This is equivalent to creating a Solaris thread in the THR_BOUND state. You can bind a thread to give it an alternate signal stack or to use special scheduling attributes with Realtime scheduling. All scheduling is done by the operating environment.
In neither case, bound or unbound, can a thread be directly accessed by or moved to another process.