The definitions in this lexicon are meant for common people, not for your teachers — and certainly not your professors. Please tune the definition into a more scientific style before you use it in class.
Fixed Costs a steady amount of expenses that have to be paid by an economic subject (household, company, the state), no matter how much they want to produce or consume. E.g. apartment rent, warehouse & office lease.
Variable Costs the expenses an economic subject (household, company, the state) has to pay depends on their production output (e.g. material costs) or in case of household, depends on their consumption (e.g. food costs)