So what exactly is a 'hardsuit'? In the LEGO universe its often a MOC that combines robot mecha and minifigure armor.
In the example shown here, builder Leg-O-Matic has designed a rather nimble rig in a jaunty pose. If you click through his Flickr stream you'll see that a full minifigure fits inside the suit acting like a suit of armor.
There are a wide variety of styles that fit into the 'hardsuit' category. There's even a Flickr photostream completely dedicated to the little buggers.
If you ever feel your minifig need that extra 'umph' to take out an adversary, or to take a trip down to the store for eggs. Try your hand at crafting one of these babies.
(Pictures from Leg-O-Matic's Flickr stream)