Several specialized usages of the terms compact and compactness exist.

• Multiple definitions of the term "compact" are found in mathematics:
  • The most common usage relates to topology, where one considers compact spaces. This article also includes the closely related notion of a compact set.
  • In order theory and domain theory the different (though not entirely unrelated) notion of a compact element is typically used.
• A Compact Flash is a type of data storage device.
• Compact car is an automobile size class in the American market.
• Compact disc.
• a British newspaper term, see compact (newspaper) .