1) Refering to 24 hours, 7 days
2) Often used as a short form to explain that a store, or shop is open all the time
3) Used as slang for something that happens often, or constantly

twenty- four hours, seven days a week.

Twenty-four hours a day, seven days a week. Alternately, 24/7/365, refering to the number of days in a year.

Constantly.

24 hours a day
7 days a week

Approximately 3.42857143

Slang for small, usually supermarket-type stores that are open 24 hours a day, 7 days a week.