It's a charateristic of a substance that during a reaction of another substance, it performs a charaterisitic.
Example: I'm Lilly, and normally I'm a normal teen. But, when my grandma comes over to visit once a year, I'm even more happier.
So, it's not the best example, but, you get the point. It's a charater when a substance or something different come to that thing, and makes it act different. Hope it helped!
