Dear NC,
Defination of leave or benefits are as per company policy which differ company to company, but, by the law, company need to certain no. of days paid leaves during the year irrespective of shops & est, or factory act.
but, as commonly below defination use for leaves.
1) Annual leave :- can be use once or twice in year (as per company policy)
2) Previlege leave :- as above
3) casual leave:- its as per company policy, you may avail any time for any casual reseaon. (but it is not boud to give by employer by the law, it optional for company)