--description--

When you want to talk about something that happens regularly on a specific day of the week, you use the expression every followed by the day.

For example, I go to the gym every Tuesday.

--questions--

What does every Monday mean?

Only on the next Monday.

This option would mean just the coming Monday.

On Monday, one time.

This choice would suggest it happens once, which is not what a regular meeting does.

On Mondays, sometimes.

Sometimes means not every time.

On Mondays, every week.