Different social networks like to call it by different names, but they're all the same really! Facebook calls it Cover Photo and I don't know what Google+ calls it but Twitter certainly introduced it as a Header Pic. Now many criticized the decision by saying that it was very much like facebook but I think it brings some sort of uniformity to what social profiles require these days! So on all major social platforms, twitter being the latest, there is an option to choose a background image to the actual Display Picture. In twitter, it can be enabled by uploading a "Header Pic" from Settings>Design. A carefully chosen header pic can earn you a lot of new followers!