A "change jar" is a jar or container where you put your loose coins and spare change. It's a way to save money in a small and easy way. Full definition
When social change jars the patterns, conventional ways of experiencing the holy disappear. (religion-online.org)
I like find all those lost coins — and sometimes dollar bills — and adding them to my spare change jar to see how fast I can fill it up. (debthelp.com)
I remember learning the value of coins and counting the pennies in the giant change jar in our living room. (policygenius.com)