What is a vulnerability called that is released before a patch comes out?

A vulnerability that is exploited before the vendor has issued a patch or even before the vulnerability

is known to the vendor is referred to as a "zero-day" vulnerability. The term "zero-day" refers to the

number of days the software vendor has had to address and patch the vulnerability since it was made

public—zero, in this case.

Reference:

Symantec Security Response, "Zero Day Initiative".