A sacrifice is a loss or something you give up, usually for the sake of a better cause. Parents sacrifice time and sleep to take care of their children, while kids might sacrifice TV time to hang out with mom and dad.
Though no longer used only in a religious context, sacrifice comes from the Latin sacra and facere, meaning "to perform sacred rites." If you've studied ancient cultures like the Incas, you've probably heard of "human sacrifice," where a person is killed in a sacred ceremony to please the gods. But thankfully those kinds of sacrifices don't happen anymore.