Heightening is an improv concept describing how performers add information to build upon what was built before.
They use this technique move the scene forward and make the events in the scene have greater consequences for the characters in the scene. This also helps connect their ideas to those added by others, to deepen character and emotion, helps raise the stakes.
"HEIGHTENING: Intensifying a relationship, a character, or a scene on stage; creating a high level of reality; giving a greater dimension to life reality; underlining life; enlargement of character or event for clarity in communicating to the audience; to make a point through heightening; using anything or everything (acting, technical, or verbal) to make an impact."
- – Viola Spolin, Improvisation for the Theater