These are the things you need to spend money on each month and the amount is usually the same. Some examples of fixed expenses are your mortgage, utility payments, daycare, gas (for your car), or a transit pass.
Then grab your bank statement or credit card bill and add expenses to your list that aren’t as regular. These variable expenses are there every month, but the amount changes.
Some examples of variable expenses are groceries, eating out, entertainment, recreation, coffees / snacks, or even cell phone bills. Variable expenses aren’t optional; you do need to spend money on them, but you have more flexibility about how much you spend on variable expenses versus fixed expenses.