What is reentrancy in JavaScript?

I would like to improve my understanding of the word reentrant.

Is this function reentrant?

function* foo() {  yield 1;  yield 2;}

And this one?

function foo() {  return 1;}

And this one?

var x = 0;function foo() {  return x++;}

And this one?

function foo() {  setTimeout(foo, 1000);}