Trees in the garden

Fruit Tree Sizes
A major factor in placing trees in the garden is the size of the tree. If heavy pruning is required then the tree is the wrong size for the garden.
A guide to terms and their sizes
Dwarf bush 0.6m
Half standard 1.35m
Standard 2m

Growing Style
Free standing
Feathered - a tree that has a single stem with lateral branches all the way to the base.
Unfeathered - a tree with a single stem- the length dictated by tree size - topped with a head of branches.
Trained
Usually against a structure - wire, wall, frame, etc:
Fan - RHS detailed article
Espalier - lateral branches are grown from a single trunk called the maiden. Vertical growth is controlled so more growth goes to the lateral spurs (branches from the maiden.
Cordon - trees are planted at an angle of 45°, no more than 1m apart (depending on plant). Lateral shoots are stubby in length so fruit is held close to the trunk. Can be vertical.
Arch - two vertical cordons grown over a structure and meet at the top.

General pruning information
Pruning is a process that needs to be timed correctly for each tree and done in the right way for the way in which the tree is being grown.
Here is a pruning overview.

Sources and Info'
Thanks to Walcot Nursery's general fruit tree info, their fruit catalogue is a great resource of info as well.
RHS has a good article with bits of useful info.
Great article on training your own trees
PDF with some good photos of espaliers