Shreya,
Compound voucher is one that is made of transactions that involve either one debit with multiple credits or multiple debits but one credit. If voucher contains transactions involving one debit and multiple credits than it is termed as credit voucher and if it involves multiple debits and one credit than it is a debit voucher.
However, a complex voucher is one that is made of transactions involving multiple credits and multiple debits. It is used to record complex transactions and is also known as journal voucher.