What does 'cut somebody some slack' mean?

[Reni]

English Grammar Tests, Elementary Level

ESL/EFL Test #132 "Conversations and Comprehension (3)", question 9

Man: Can you believe the way John acted last night? He's really lashing out at everyone lately.
Woman: I know. He's really stressed about losing his job. We should cut him some slack until his situation improves because he's normally not like that at all.
Narrator: What does the woman imply? .........

(a) She thinks John is intelligent and will find a job soon.
(b) She thinks John is behaving badly and they should stop seeing him until his behavior improves.
(c) She thinks they should excuse John's behavior because he's under a lot of stress.

English Grammar Tests, Elementary Level

ESL/EFL Test #132 "Conversations and Comprehension (3)", answer 9

Man: Can you believe the way John acted last night? He's really lashing out at everyone lately.
Woman: I know. He's really stressed about losing his job. We should cut him some slack until his situation improves because he's normally not like that at all.
Narrator: What does the woman imply? She thinks they should excuse John's behavior because he's under a lot of stress.

Correct answer: (c) She thinks they should excuse John's behavior because he's under a lot of stress.
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Could you explain me what means exactly "cut sb some slack"

[Mister Micawber]

cut/give (someone) some slack (Slang) To make an allowance for (someone), as in allowing more time to finish something.
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Native English teacher at Mister Micawber's