"Leave" is vacation time, or "time off." I assume the sentence means that if you only work for part of the year (a "partial year"), you will get vacation time that is proportionate to the amount of time you worked. For example, instead of working for twelve months and getting four weeks of vacation (12:4), you may work for six months, and get two weeks of vacation (6:2).

It means the number of leave days are calculated as a proportion of the days the employee worked in that year. I hope that helps. 😊

Does it means prorated?