To be petty means to be overly concerned with small, trivial, or unimportant matters, often in a way that is spiteful, narrow-minded, or small-minded. It involves focusing on minor issues, sometimes to the point of making a big deal out of insignificant things or holding grudges over them. This behavior often comes across as unfairly harsh or mean-spirited about matters that do not really deserve such attention or reaction. Additionally, petty can also refer to something that is minor or of lesser importance, such as a petty crime or petty official, without necessarily having a negative connotation.