Week most generally refers to any period of seven consecutive days.

The word week also commonly refers to the seven-day period that begins on Sunday and ends on Saturday (though in some places this may be different, with the week considered to begin on Monday, for example). There are 52 of these weeks in a calendar year.

Sometimes, the word week is used to refer to a seven-day period that begins or includes a specific day, as in the week of September 5 or Thanksgiving week. 

It can also be used to refer to a seven-day period dedicated to a specific cause or cultural observation, as in National Grief Awareness Week.

The word week is also often used to refer to the workweek (or schoolweek) to distinguish this span of (often five) days from the weekend. The standard workweek is from Monday through Friday, with Saturday and Sunday being considered the weekend, though working schedules vary widely. Many full-time jobs consist of a 40-hour week (five eight-hour days).

The days within this five-day span are called weekdays, and the evenings of those days are called weeknights. The middle of the week is called midweek.

The word weekly most commonly means done or happening once a week or every week, as in a weekly meeting. 

Example: They said it would take a week to get a reply, and it’s been six days already, so I’m hoping for a response tomorrow.