iptables rule for ftp

Hello,
Can anyone explain what this rule means..

iptables -A INPUT -p tcp --sport 20 -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -A OUTPUT -p tcp --dport 20 -m state --state ESTABLISHED -j ACCEPT

This is the rule for active ftp connection tracking. In active ftp, shouldnt the server port (data port) be 20? With this concept in mind, I cant figure out what the rule means.. Any help is appreciated..

 

 

 

 

Top