A Teaching Unit is a cluster of several lessons that fit together closely. The lessons of the unit will address the same essential questions and will help the students learn the same enduring understandings.
With other words, a Teaching Unit is a well-defined thematic body of instruction. It has a single instructional goal with several supporting objectives. It has a beginning, designed to focus interest, and an ending, designed to test for accomplishment. Each activity should insure success of the single instructional goal.
Don’t forget a mention for the attention to diversity.