A chain can be any of the following:

• a flexible connection through multiple rigid links; applications include:
  • pulling (it can not be used for pushing)
    • power transmission, as in roller chains (e.g., bicycle chains)
    • conveyance systems, similar to a conveyor belt, as in flat chains and pintle chains ;
  • keeping together to avoid falling apart, drifting away, theft, fleeing (of a prisoner)
  • jewellery
• In mathematics
  • a chain in algebraic topology is formal linear combination of k-simplices.
  • a chain in order theory is totally ordered subset of a partially ordered set;
• a measure of length used in surveying and equal to 22 yards (also called the surveyor's or Gunter's chain);
• a measuring instrument used in engineering, also called the engineer's or Ramsden's chain (and rarely, its length of 100 ft as a unit of measurement, though the results of the measurements are normally expressed in feet); or
• a franchise of stores, restaurants, hotels, or other retail establishments.
• a type of armor made of interlocking chain links, better known as chainmail.

See also Chain of command.