How do I call this interaction?

There's this interaction on Airbnb (example page: https://www.airbnb.com/rooms/432044), where the section containing the price, "Request to Book" call to action, etc. on the right are scrolled with the content, but only until it reaches top of the screen. Can you help me with finding a good name for this type of interaction (whether on web or for mobile products/websites)? I'm looking to write an article about this type of interaction, and wouldn't want to describe it as I just did above each time I'm referring to it.