Used as a noun or adverb meaning each day without exception. Very common in everyday speech.
I take a walk every day.
毎日の習慣は大切です。
Daily habits are important.
He keeps exercising every day.
I go to school every day.
Lately, every day is fun.
毎日 means 'every day' as a straightforward time expression, whereas 日常 describes the quality or texture of everyday life rather than counting the days.
毎朝 refers only to mornings, whereas 毎日 covers the whole day and is broader in scope.
毎日 simply means 'every day', while 朝晩 points specifically to the two daily times of morning and evening, as in taking medicine twice a day.