-apm (action per minute) is a command in Dota-Allstars which tells Action Per Minute of your Character and your Summoned units
People who have an APM of 200 in DotA are silly. There's no reason whatsoever why you should be making one single unit perform that many actions.Anything around the 70-120 range is enough for DotA but keep in mind it has no correlation with skill still.
Sometimes it depends on the hero. Some heroes require more clicking. With Luna I tend to get 100 APM or so. Just from clicking on the ground so much and controlling all my dominated creeps and that's IF I have creeps. Now Silencer, that is a very apm intensive hero imo. Rexxar is another one. Control Hawk and Boar at the same time.
The thing is with some heroes like Chen and Meepo even noobs can get a high apm because when you select 4 meepos and right click once that counts as 4 actions. That's where some of the ridiculously high apm numbers come from (not that a pro couldn't get 200+ with any hero but it's mostly unnecessary).
On the other hand a good Meepo or Chen NEEDS a high apm in order to be effective and the apm difference between an auto-attacking noob and a skilled player that moves in for last hits, moves back again, cancles his attack animation just to make his opponent attack too early and generally keeps moving not to be an easy target for heroes like PotM or Pudge is HUGE.
It's not like high apm = pro, low apm = noob but with 50 apm you really can't be doing well, 90 seems pretty low as well but I've seen pros having around 90 in some games, sometimes a high apm is just not needed as the people above me said.