SSL (Secure Socket Layer) is an internet protocol providing a secure connection between a web browser and a server.
A security certificate (also called SSL) helps one computer understand that the other computer trying to communicate with it is legitimate or safe. Security certificates help keep data safe during transmission over the internet.
Google announced in 2014 that it would be using SSL as a ranking factor in search. In other words that mean if you have a security certificate applied to your domain, Google uses that signal to place you above other sites that may not have that feature (all else being equal of course).