X-Efficiency - A concept introduced by economist Harvey Liebenstein. A company's ability to use its workers, machines, technology, etc., to produce maximum output at lowest cost and as quickly as possible.

Xenology - The scientific study and/or research of alien cultures and biology.

Xerox Machine - A piece of equipment which makes paper copies of documents, etc.

X-Inefficiency - When a company is not using its employees, machinery, resources, etc., effectively, often because of lack of competition.

Xylography - The art of engraving an image on a block of wood, or printing from woodblocks.