A weighted average is an average resulting from multiplying each component by a factor indicating its importance.
Example: Many of your teachers probably use weighted averages to calculate your grades: homework might be worth 20%, participation 20% and tests 60%, for example. If Angela has a homework grade of 98%, participation grade of 90%, and test grade of 82%, her final grade would be (0.20)(98) + (0.20)(90) + (0.60)(82) = 86.8.