What does "day in day out" mean?

[PenniK]

English Idioms and Expressions, Intermediate level

ESL/EFL Test #5 "As happy as the day is long", question 3

Yes, we went away on holiday last week but it rained day in day out.

(a) every single day
(b) every other day
(c) every second day
(d) every two days

English Idioms and Expressions, Intermediate level

ESL/EFL Test #5 "As happy as the day is long", answer 3

Yes, we went away on holiday last week but it rained every single day.

Correct answer: (a) every single day
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please need to know what does it mean ?

shery

[Lost_Soul]

Are you sure that it reads "day in day out"

I've heard a lot of "day in and day out"

[Mister Micawber]

.
DAY IN, DAY OUT
.
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Native English teacher at Mister Micawber's

[Yankee]

Hi LS

The expression is very often (probably most of the time) used without the word 'and'. However, as far as I know, without the word 'and', there should always be a comma:

day in, day out

[Lost_Soul]

Oh, yeah, you're right.
Lingvo let me down once again