a monopoly-supplied service, facility or function that a competitor requires as an input and that it cannot duplicate economically or technically
a service, facility or activity of the Government of Canada that is or will be, at any time, necessary for the safety or security of the public or a segment of the public
A service without which a building would be ‘disabled'. Often applied to the utilities (water, gas, electricity, etc.) it may also include standby power systems, environmental control systems or communication networks.
of electrical power supply on board a ship, it refers to emergency power supply to services that is essential to the safety of the ship and crew during a total power failure; essential service may include emergency lighting, alarms, communications, etc.
In telecommunication, an essential service (critical service) is a network-provided service feature in which a priority dial tone is furnished. Essential service is typically provided to fewer than 10 % of network usersm, and recommended for use in conjunction with NS/EP telecommunications services.