What is the meaning of Reentrant?

Reentering; pointing inward.

Such that the corresponding lock can be reacquired by the locking thread.

That may be executed more than once at a time either by different threads, or because of recursion.

Designed to return to the Earth's atmosphere.

Of or pertaining to reentry (in the heart).

Having the strings not ordered according to pitch (having a re-entry).

An angle or part that reenters itself.

One who enters (the labour market, etc.) again.

A valley between a pair of parallel ridges.

Source: wiktionary.org