Meaning and usage of the word "slip"

[Ketty]

English Synonym, Elementary Level

ESL/EFL Test #72 "Synonyms for mistake and error", question 6

Sorry, I didn't mean to say this, it was a ......... of the tongue.

(a) slip
(b) mistake
(c) fault
(d) error

English Synonym, Elementary Level

ESL/EFL Test #72 "Synonyms for mistake and error", answer 6

Sorry, I didn't mean to say this, it was a slip of the tongue.

Correct answer: (a) slip

Your answer was: incorrect
Sorry, I didn't mean to say this, it was a mistake of the tongue.
_________________________

please,

explane the meaning and usage of the word "slip"

Thanks in advance
Ketty :)

[Conchita]

'A slip of the tongue' is a set phrase which means 'a mistake in speaking'.