Meaning of trace space

Hello Coreform! In the U-spline paper on your website, what is the meaning of a “trace space” found in section 4.3? Where can I read more about this concept?

Hello, kaba! I’m sure that others may have more resources on this, but I found the wikipedia page on the Trace operator to be helpful on the topic:

The trace is basically the restriction of a function to the boundary of the domain over which it is defined.

Thank you, Caleb. This seems to be the answer.