Which term is defined as an exploit that takes place before the security community or software developer knows about the vulnerability or has been able to repair it?

A zero-day attack.

Explanation:

A Zero-day vulnerability is a computer-software vulnerability that is unknown to, or unaddressed by, the security community or software developer or even the vendor of the target software. Until the vulnerability is mitigated, hackers can exploit it to adversely affect computer programs, data, additional computers or a network.

An exploit directed at a software with zero-day vulnerability & exploiting this vulnerability is called a zero-day exploit, or zero-day attack.

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