What is the difference between Firewall and ACL?

ACL is part part of  Firewall. And Firewall is a whole security package. 

Firewall is a complete network security device or software that monitors and filters incoming and outgoing network traffic based on the security policies applied. 

An access control list (ACL) is a list of rules that specifies which users/systems/IP's are allowed or denied access to a particular system resource or network.