Stands for Highly Sensitive Person. Refers to people who are oversensitive to sensory aspects of their environment/world. For instance, HSPs may hate harsh lighting, or get really annoyed by background noise. HSPs can be very irritable and easily annoyed as a result.
Lisa is such an HSP, she gets annoyed so easily. She kept complaining about it being too bright in the restaurant, and she kept talking about her sweater being too itchy!