Learner's definition of WEEK
1 : a period of seven days
◊ In the U.S., a week is usually considered to start on Sunday and end on Saturday, while in the U.K. a week is usually considered to start on Monday and end on Sunday.
the last week of the month
I can meet you sometime next week.
The menu changes each/every week.
I volunteer at the school once a week. [=once every week]
You can never be sure what will happen from one week to the next.
2 [count] : any period of seven days in a row
The baby is two weeks old. [a two-week-old baby]
I'll be on vacation for two weeks starting this Tuesday.
That car rents for $200 a/per week.
We'll leave a week from today. [=seven days after today]
I arrived a week ago.
It took him two weeks to paint the house.
Sometimes he's away for weeks at a time.
The doctor said he wants to see me again in a week. = The doctor said he wants to see me again a week from now. = The doctor said he wants to see me again in a week's time.
3 [count] : the days from Monday through Friday when people usually work
We're open from 9 to 5 all week.
He earns $500 a week at his job.
I'll be working next week.
He has a 40-hour work week.
week in and week outalsoweek in, week out
: every week for many weeks : for a long time without stopping or changing