Expansion

noun

1. The act or process of expanding.

   "The expansion of metals and plastics in response to heat is well understood."

2. The fractional change in unit length per unit length per unit temperature change.
3. A new addition.

   "My new office is in the expansion behind the main building."

4. A product to be used with a previous product.

   "This expansion requires the original game board."

5. That which is expanded; expanse; extended surface.