In the same sense as your server has an "energy consumption" of 2000W, i.e. 1W <=> 356*24/1000 kWh/a.

By saying they use 6kW I mean that each year they use 6kWa (kilowattyears), or 52569 kWh. And 6 kilowattyears per year is the same as 6 kilowatt.