Energy clearing is a way to remove unwanted, negative energy from people, places, and things. Everything is made of energy including thoughts, feelings, and emotions. Objects, buildings, and locations can have energy imprints, residual from past events and people.
Sage/smudging is one of the most well known clearing tools but there are many others that may be more appropriate to the situation.
“Everything is energy and that's all there is to it. Match the frequency of the reality you want, and you cannot help but get that reality. It can be no other way." -Albert Einstein