Welcome to the board Vasbyte! A MHD is a Mexican Hat Dance, a fun and profitable way to stick it to the airlines, in the words of one its inventors, Ken hAAmer above.

If you search this forum using MHD you will find a number of threads that outline in detail what it is. However, it is basically a way to get cheaper flights across Canada by travelling via Mexican locations.

The most avid MHDers seem to be Ken, Blondebomber, and MapleLeaf, who was written up in the Globe a couple of weeks ago. My apologies if I forgot anyone.