What is CTR?

CTR stands for the abbreviation for click through ratio. It is defined as the total clicks by a user on an advertisement posted on a website to the total number of visitors who visited that website. The more this ratio is the higher are the chances that more percentage of total visitors will visit a certain website. CTR therefore is the best way to define the audience being pulled out of the total from a website. CTR provides the guideline for the traffic diverted towards the desired website from another website and helps make major decisions in improving the overall network traffic towards website. If CTR is 2% that means that out of 1000 visitors visiting a site only 20 are being pulled towards that particular site through the links given on the other site. 
What is FFA?