A vehicle composed of basically an engine, a tank, and a pair of wheels. Often have excellent power-to-weight ratio and heaven sent fuel-consumption.
Not necessarily a sportsbike (refered to as "crotch rocket" by those who can't get their momma to buy them one, or can't get any).
Comes in various forms, from a cruiser (terminator bike), dual-purpose bikes (badass bike, typically used by the villains in a movie, eg: KLR650) to naked bikes (father of the sportsbike, mother of all bikes, eg: Bandit 1200, Ducati Monster).
Unfortunately, sometimes it is operated by attention whores, monkeys, or people with small dick. These are the ones you see riding recklessly on the freeway, often wearing nothing more than a helmet, a t-shirt, and a pair of flip-flops.
Sometimes used as a benchmark for accelaration by ignorant petrolheads, such as that kid driving his mom's civic who thinks he's the shiet when passing one, or that whiny british car journalist.
Bob sees a motorcycle cruising at traffic speed on the highway.
Bob : Look, a motorcycle. I will overtake him to show l33t I am.
Bob overtakes the motorcycle, on the wrong lane, at twice the speed limit, with blinkers off.
Bob : he didn't have a chance. haha. Oh, my dick is 4 inch longer now. w00t.
Motorcyclist who was cruising at 1/8 throttle : Sigh. Poor kid. I guess american education is to blame....