[vnfmsthf430]

what is {h}?

[spiderstar]

It's one of the many commands in the game.
{h} basically makes the sector map harder by increasing the damage of the mobs/bosses and the health but gives you more xp. 

[Xkiller712]

It makes the game harder, but gives 2x exp.

[RedNeon]

does h works on survival too

[Nucleaon]

Yes