noun

• (countable) A series of links united; a series or order of things depending on each other, as if linked together; a chain, a succession.
  "Try and penetrate with our limited means of the secrets of nature and you will find that, behind all the discernible concatenations, there remains something subtle, intangible and inexplicable."
• (uncountable) The application of these series of links.
  "We also discuss the faults to which the intermediate systems that execute these concatenation tasks are liable; the consequences of such faults include end-to-end PDUs being misforwarded, proliferating without limit, or simply disappearing into “black holes.”"
• (programming) The operation of joining multiple character strings.
• (programming) A character string formed by joining multiple character strings.