In TF2, Pyroshark is the name given to the Pyro playstyle of using the Neon Annihilator, and hanging out in places like the sewers on 2Fort, the middle section of Well, or near the middle point on Powerhouse.
This is because the Neon Annihilator crits target that are
wet (In or just exited
water) so players who use it hang out on maps with
water areas exclusively near those areas, hence, Shark.