Consumption means using, buying or eating something. If we don't reduce our energy consumption, we will run out of fuel. Conspicuous consumption is buying something to show off.
Consumption is related to the verb consume, which means to eat, use, or buy. You will often read about consumption in terms of rate––how fast we are using up a particular resource. If you consume ten cookies in an hour, your rate of consumption is ten cookies an hour. Sustainable? Let's hope not.