Magnitude of 2x2 matrix meaning?

I've been asked to find the magnitude of a strain tensor, but I don't know what that signifies. Does it mean determinant?

Randy P2014-11-08T14:53:36Z

According to this page:
http://www.foamcfd.org/Nabla/guides/ProgrammersGuidese3.html
|T|^2 is something called the "second inner product" of T with itself, and that is defined. Look for "inner product" and "magnitude" on that page.

However, I have a hard time believing you would be asked to calculate something which is not defined in your textbook and in class.