POSIX Threads is a POSIX standard for threads. The standard defines an API for creating and manipulating threads.
Libraries implementing the POSIX Threads standard are often named Pthreads. Pthreads are most commonly used on Unix-like POSIX systems such as Linux and Solaris, but Microsoft Windows implementations also exist. For example, the pthreads-w32 is available and supports a subset of the Pthread API [1]. (Note: in text, Pthreads is written with an upper-case P.)

Example

David R. Butenhof: Programming with POSIX Threads, Addison-Wesley, ISBN 0-201-63392-2
Bradford Nichols, Dick Buttlar, Jacqueline Proulx Farell: Pthreads Programming, O'Reilly & Associates, ISBN 1-56592-115-1
Charles J. Northrup: Programming with UNIX Threads, John Wiley & Sons, ISBN 0-471-13751-0