BMX stands for Bicycle Motorcross and began back in the late 1970s.
The sport has gone through many ups and downs and changes over the years, but today there are five main disciplines.
These disciplines are split into two sections - racing and freestyle.
BMX racing is quite self-explanatory but the freestyle heading has four different disciplines which take a bit of explaining.
Riding street is just what the name suggests - finding an everyday urban obstacle and doing tricks on/over it.
Street (and ramp) bikes used to be ridiculously heavy.
When people started to ride freestyle, they used race bikes which would fall apart as soon as they looked at a ramp.
To combat this, bike companies made bikes that were built like tanks. They wouldn't break, but you couldn't really do anything on them either.
Nowadays, it's the fashion to have your bike as light as possible - but it all comes down to the old strength-to-weight question.
Basically, you want a bike that's light enough for you to do stuff with, but not so light that it breaks when you try and grind a ledge.
Street bikes usually come with pegs and a gyro. Nowadays, many people just have one set of pegs, on their favourite side.
However, many street riders choose to ride with four pegs and no brakes.
Everyone likes their bike set up a different way - BMX is all about freedom and self-expression, so don't worry if your set-up is different.
Flatland involves doing tricks on your bike while on a flat piece of ground.
And it's even easier than street for finding places to ride.
Riding flat takes a lot of practise and flatlanders tend to be a funny little crowd.
They like to spend long hours in car parks or on tennis courts, riding alone and listening to tunes.
Flatland bikes are very short and light, making them spin easier. They also have four big, fat pegs that are used to stand on.
Most flatlanders use a gyro with front and back brakes.
However, some only use a front brake and some use none.
Dirt jumping is split into two different forms: 'trail riding' and 'dirt jumping'.
'Trails' is used to describe a collection of dirt jumps.
Trail riders generally prefer to spend their time in the woods, building more and more jumps that link all over the place for them to flow through.
'Dirt Jumping' is basically what you see at the X-Games where there are two or more huge jumps and riders try and do as many tricks over them as possible.
Dirt bikes are generally heavier than a race bike, but lighter than a street bike (although they can be used for both if you're smooth enough).
A dirt bike will usually have no pegs and may or may not have a gyro.
Dirt riders also tend to use wheels with 36 spokes which are lighter than street wheels and they use race-style two piece-bars.
RAMP AND PARK
This involves riding and doing tricks around a specially-designed ramp park.
Ramp parks can be made of concrete (nice), wood (nice) or aluminium (horrible, scary and dangerous).
When you first go to a park, don't just drop in and hog the park - remember to take your turn and let other people ride/skate.
Bikes for riding ramps are basically the same as those used for riding street.