Continuously; from beginning to end; all the time. Often used to mean something happens repeatedly or without interruption.
彼は始終元気で、どんなときも前向きだ。
He is energetic all the time and positive no matter what.
始終文句ばかり言っていると、周りの人が疲れてしまう。
If you keep complaining all the time, the people around you will get tired.
会議中、彼女は始終ノートを取っていた。
She was taking notes throughout the meeting.