"720pflixlol" is a domain name associated with a network of unauthorized streaming websites. The nomenclature follows a common pattern used by "pirate" streaming sites: referencing video resolution ("720p"), a brand ("flix"), and a casual suffix ("lol").
Many ISPs actively monitor traffic to known pirate domains. They may send you a "copyright infringement notice" and, under a "six-strikes" policy, throttle your internet speed or terminate your service after repeated violations. 720pflixlol