SuMo: like rump says, 17s and sportbike-sized brake discs on a motocrosser, enduro or dual sport. May be street legal or not, may be homemade or factory built. Look for a DRZ400SM as the poster child here.
Enduro: I think today it means a trial-riding model like Honda's CRF450X or the Yammie WR250F. In the old days it meant a dual-sport, but today even though it has marker lights that look like headlamp/tail light, not street legal. So it will have full knobbies not intended for pavement.
Motocrosser: lighter, race-oriented version of an enduro that is for closed-course motocross racing, although you see them on trails. CRF250F is a good example.
Dual-sport: a road-legal Enduro, so all its equipment is a compromise between street and dirt, which, as Rump sayeth, means it sucks at both. The most popular dual-sports are better for street than dirt, but are still very fun and capable on graded, easier sorts of trails: KLR650, DR650, BMW GS series.
Adventure-Tourer: a large, heavy, fast and comfortable bike the looks like a dual-sport but is really best on pavement. Some of these whales are over 600 pounds, but some, like the KTM Adventurer are actually pretty good off road, or so I'm told--my off-road skills are pretty minimal.