「毎日」(mainichi) means "every day." It indicates an action or event that happens on a daily basis, regularly. It's often used with habitual actions. For example, 「毎日、日本語を勉強します」(Mainichi, Nihongo o benkyou shimasu) means "I study Japanese every day."

「毎(まい)日(にち)」は「every day」という意味(いみ)です。毎(まい)日(にち)繰(く)り返(かえ)す行(こう)動(どう)や習(しゅう)慣(かん)を表(あらわ)す時(とき)に使(つか)います。例(れい)：「毎(まい)日(にち)、日(に)本(ほん)語(ご)を勉(べん)強(きょう)します」。