The word "grump" is an informal term used to describe a person who is in a bad mood, irritable or surly. A grump may be easily annoyed by others and may express their displeasure through negative body language, such as frowning, scowling or slouching. Grumps are often difficult to interact with and can bring down the energy of those around them. The term "grumpy" is also used to describe a person's behavior when they exhibit these traits consistently over time.