& in linux code example

Example: what is :(){ :|:& };: command?

#     _______      _________      _____       ______     _
#    / _____ \    |____ ____|    / ___ \     | ____ \   | |
#   / /     \_\       | |       / /   \ \    | |   \ \  | |
#   | |               | |      / /     \ \   | |   | |  | |
#   \ \______         | |      | |     | |   | |___/ /  | |
#    \______ \        | |      | |     | |   |  ____/   | |
#           \ \       | |      | |     | |   | |        | |
#    _      | |       | |      \ \     / /   | |        |_|
#   \ \_____/ /       | |       \ \___/ /    | |         _
#    \_______/        |_|        \_____/     |_|        |_|
#DO NOT RUN THIS IN LINUX TERMINAL OR ANY TERMINAL IT IS A DEADLY COMMAND

:(){ :|:& };: