It sounds fancy and looks a bit complicated but all the term espalier means is the process of training trees and shrubs against a flat surface, such as a wall, fence or trellis, with branches tied in horizontally against the support in a pattern of your choice. This looks beautiful as the branches fan out on the wall and in addition a plant pruned this way uses far less space, which means it's ideal for small gardens and narrow spaces where trees that spread will not fit.
An espaliered design uses a main vertical stem from which side branches are trained in tiers to achieve the shape you want and it only takes a couple of years for the basic shape to get established, with more intricate designs taking longer. Another big plus is that an espaliered tree only requires light annual pruning to keep it in shape but it's important to do this to keep the structure looking good.
