A conversion can be any of many different actions that the end user does in your Protected Page: click on a button, subscribe to a newsletter, fill-in a form... in short, a conversion is any action on your Protected Page where fraud might happen.
From Opticks perspective, a conversion is a call to the conversions endpoint in a way that a postback is executed.
It is very important to analyze the behaviour of the end-user (or maybe the fraudulent bot) pre-conversion as an additional layer of security.
Opticks is able to use this extra layer of security analysis to detect and block fraudulent conversions.
If you have not done it already, you should inform Opticks of the conversions on your protected page in order to get more useful data and also a new layer of security.