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