Deck = Decks are usually made of maple plywood, 7 plys thick. These days, we have decks that are made of 8 or 9 ply. Real skateboards are scooped out like a dish, the dishlike attribute is called a concave. Concave increases the strength of a board and also help skaters position their feet for a trick. Shallow concaves are good for streetstyle and technical tricks. Deeper concaves are used normally for ramps. The width of a deck ranges from 7.5" to 8" and the length ranges from 30" to 32". Of course, there are smaller decks available for younger kids as well.
Trucks = Trucks carry the heavy load. They provide adjustable steerage and at times, serve as a grinding surface.
Wheels = Wheels are made out of urethane, not plastic. Wheels come in different sizes and degree of hardness. Small wheels provide quick acceleration and are ideal for streetstyle. Big wheels are good for speed and control and are ideal for ramp tricks.
Bearings = Most bearings have a ABEC rating. ABEC is the acronym for Annular Bearing Engineering Committee, the standards committee of the Anti-Friction Bearing Manufacturers Association (an industry group) that determines the requirements for each level of bearing precision. Abec Bearings are rated in odd numbers i,e; Abec 1,3,5,7,9. Beside ABEC bearings, there are also swiss bearings, 6 ball bearings, titanium bearings, ceramic bearings etc. These bearings are generally more expensive.
Cushions/Bushings = Cushions allow the trucks to pivot and turn smoothly. Cushions comes in different hardness; soft, medium, hard and extra hard. If you feel that your truck 'wobbles' no matter how much you have tightened it, it might be your cushion!
Base plate = Baseplate is the component that connects the trucks to the deck using bolts and nuts.