ex·pan·sion 
(ĭk-spănshən)
(ĭk-spănshən)n.
1.
a. The act or process of expanding: the new nation's expansion westward.
b. The state of being expanded.
2.
a. An expanded part: an expansion of a river.
b. A product of expanding: a book that is an expansion of the author's PhD thesis.
3. The extent or amount by which something has expanded.
4. Mathematics
a. A quantity written in an extended form, such as in a sum or product of terms.
b. The process of obtaining this form.
5. An expanse.
6. A period of increased economic or business activity.