An Asteroid is an object made primarily of rock or metal which can be found orbiting the Sun in a belt called unsurprisingly – the asteroid belt. It’s located between Mars and Jupiter. Many of the asteroids are really quite big – in fact Ceres has a diameter of nearly 600 miles – they are often referred to as minor planets or planetoids due to their size.
As for the smaller asteroids, well there are simply millions of these. The very small ones are known as meteoroids and are made up from the very same material as the bigger asteroids. In fact it is thought that these are made up from material which was created at the time when the planets were formed.
There are other even smaller objects called meteors which are actually only dust size particles. Because they are so small they completely burn up when they penetrate the Earth’s atmosphere. As such you’ll only find metorites on the planet as they are big enough to survive.
If you want to know more about meteors and asteroids then I suggest the Solar System section on the BBC website is an excellent place to start. There’s lots of programmes such as “What is a Meteor”, and one of my favourites by Patrick Moore where he talks about the Perseids and the wonderful light show they create. If you have trouble watching BBC Iplayer due to your location you can read this post on how to use a BBC proxy. It’s actually just a method to route your connection through a UK proxy so you don’t get blocked.