Notes API: Maximum size of a bbox?

Hello,

I want to write a small script using the Notes API. I want to limit the size of a Bounding Box that a user can choose. So if I try big requests OSM Servers are repsonding:

[400] The maximum bbox size is 25, and your request was too large. Either request a smaller area, or use planet.osm

What does 25 mean? 25 square kilometers?

Thanks in advance!