A microclimate is the climate of a small, specific place within an area as contrasted with the climate of the entire area, or the "macroclimate." The climate of the entire area is indicated by where a region lies in the USDA Plant Hardiness Zone (simply "zone" for short). - ref. from about.com
Each year I become more and more aware of the many microclimates within my own yard. This time of year is is a good time to check your plants as they begin to bud out and how different each area of your yard progresses. By knowing a few basic things to look for, you will be able to choose better locations for your plants, shrubs and trees.
I always love a good demonstration on what that means, so when I found this I had to share it!
Cornell University has written a wonderful article on recognizing and dealing with microclimates and is worth your time to read.
Strolling through my yard, I can see the results of using some of these factors in where I place certain plants. I definitely take advantage of my southeast corner close to my home for planting certain things that are more prone to freezing temperatures. I will also make sure I keep my apple trees and other plants that require "chilling hours" out away from items that store heat. There are other things such as hills and valleys that also need to be treated differently. It has even been mentioned that having a privacy fence in your backyard creates a microclimate due to wind circulation and holding heat inside. Now I need to go out to do some more investigating!