I have to know the Explanation for DoS IPtables Rule.?

Guys I have trying to prevent my system from DoS attack. I google it, and find a IPtables code. But i don’t the meaning for this code. What the rule was doing.? Please tell me clearly About the Rule.

iptables -A INPUT -p tcp --dport 80 -m limit --limit 25/minute --limit-burst 100 -j ACCEPT

I want to know what is the meaning for this : limit --limit 25/minute --limit-burst 100

Hi,
‐‐limit rate: Maximum average matching rate: specified as a number, with an optional ‘/second’, ‘/minute’, ‘/hour’, or ‘/day’ suffix; the default is 3/hour.

‐‐limit‐burst number: Maximum initial number of packets to match: this number gets recharged by one every time the limit specified above is not reached, up to this number; the default is 5.