Backward Design is exactly what it sounds like -- you construct a course from the back to the front basing your instructional choices, patterns, and strategies on your end vision of your students. Therefore, the first step in this process is to create your end vision of your learners as they leave your realm of influence. Here you ask yourself a series of pertinent questions like -- what will they know how to do, and at what level of mastery? As you proceed through the course development processes, you continually test what you are doing against your end vision of the learner.
Here are more details on the process.