"Leave" is a break from your job. There are several different types of leave:
- sick leave
- vacation leave
- maternity leave
"Maternity leave" is time that women get off of work when they have a baby. Depending on the country and company, the length of maternity leave can range from a few weeks to over a year.
When a person is taking leave and isn't at work, you describe them as being "out on leave":
Sorry, but Mr. Schumacher is out on sick leave.