For people who don't know what "lurking" is, it's basically a more strategic version of what some might call "camping" from CS. In CS, you have to attack one of two sites, so you commit most of your team to moving into a site/position and then you leave a lurker in an odd spot that the enemy team is likely to rotate through to answer your push. In OW, it works differently since there is only one objective, but you can get the idea with how the map paths and mobility works. It's not exactly flanking and being aggressive, it's more like defensively hanging out in spots where you might pick up picks on people like Tracer or Lucio or whatever.
Roadhog used to be pretty good at this early on when guys like Hymzi and Harbleu were the only ones playing him, before Ana turned him into a frontline DPS. Nowadays characters like Genji mostly do this by hanging out over entry ways and swift striking back into safety during assassination attempts.
Turns out Doomfist is really good at doing that and he also has tank displacement + the ability to snowball harder than Genji.
