expansion

noun

• The act or process of expanding.

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

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

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

• A product to be used with a previous product.

  "This expansion requires the original game board."

• That which is expanded; expanse; extended surface.
• (steam engines) The operation of steam in a cylinder after its communication with the boiler has been cut off, by which it continues to exert pressure upon the moving piston.