The second day of the week in many religious traditions, and the first day of the week in systems using the ISO 8601 norm. It follows Sunday and precedes Tuesday.
"Monday is recognized as the second day of the week in most religious calendars but serves as the official start to the workweek under the ISO 8601 standard."
In plain English: Monday is the first day of the workweek that comes right after Sunday and before Tuesday.
"I usually go to work on Monday mornings after I buy my coffee."
on Monday
"I will finish my homework on Monday."
Monday comes from Old English, where it originally meant "day of the moon." This name was adopted by Germanic speakers as a direct translation of the Latin phrase for the lunar day.