Bonsai trees are special miniture trees that grow indoors (usually) in pots.
Bonsai is japanese for 'potted plant' and originated in China. they are absolutely gorgeous, the idea of having an entire tree on your windowsil amazes me till today, they grow like trees for years and years,
there are several styles and types of bonsai:
The formal upright style, or Chokkan, is just as the name suggests, and is characterized by a straight, upright, tapering trunk. The trunk and branches of the informal upright, or Moyogi, may incorporate pronounced bends and curves, but the apex of the informal upright is always located directly over the roots.
Mr Myagi from the movie Karate Kid was the first person to get me interested in Bonsai trees. In the movie he talks about how precious they are and how they needed to be treated carefully, and can be shaped by cuttings to control their size.

My Bonsai adapts within two days to changes in positions of light (the stalk/branches always bend towards the light for efficient photosynthesis - and growth)
My bonsai also has some arial roots and completely holds all the soil in its tiny pot, it grows incredibly quickly and can be cut into shapes by cutting the branch with scissors just below a new leaf.
I mentioned earlier how a mini tree facinates me, as tree's provide massive amounts of biodiversity. I actually once found two mini snails living in the soil around my bonsai tree! and there is always moss and certain fungi that grow around the bark (not because i overwater the plant!) I have re planted cuttings which sucesfully grow, now my pot looks beautiful with mini 'poles' growing around my tree(poles being the cut branches) Trees are great for rooms as they not only make the room more attractive but provide plenty of oxygen when photosynthesising. As Bonsai are so precious people use special soils information of which can be seen here: http://en.wikipedia.org/wiki/Bonsai
However I used natural soil from my garden and my bonsai is thriving, Bonsai are tree's that are dwarf so are strong and able to survive more extreme conditons than plants would, due to their transpiration stream to cool themselves in hot weather it is important they are watered and the bark should not dry out.
In summer you can keep the bonsai in the garden, I did this growth was very rapid, but the soil dried very quickly and often the leaves would appear to burn and die quicker. According to instrucions, bonsai should be kept away from direct sunlight and extreme heat, they are indoor plants.