The phrase "nice thing" is an expression that refers to something positive, pleasant or kind. It can be used in a variety of contexts such as describing an action, object or situation that brings happiness, satisfaction or joy. For example, one might say "It was a nice thing for him to bring me flowers after I had been sick." In this case, the act of bringing flowers is being referred to as a "nice thing" because it brought comfort and kindness to the person receiving them.