It is also called a "Corner return".
This website might help with some terms.
Building Construction & Finishing
Most of this information comes from a book called "Modern Carpentry" by Willis H. Wagner & Howard Bud Smith, 2003. ISBN # 1-59070-202-6 Publisher is The Goodheart=Wilcox Company.
It is a book that I use all of the time when it comes to questions about light construction.