polog

1. (in banking, as security) deposit; security deposit
   Dnevni polog moram da odnesem u banku do pet. — I have to take the daily deposit to the bank by five.
   Gotovinski polog na račun je besplatan. — A cash deposit into the account is free of charge.
2. (in poultry keeping) nest egg left to encourage laying
   Baba uvek ostavi jedan polog u gnezdu da kokoške ne nose po dvorištu. — Grandma always leaves one nest egg so the hens don't lay all over the yard.

In everyday speech about savings, people more often say "depozit" or "štednja", and "kaucija" for a security deposit; "polog" is typical of banking paperwork.