When a cadet at West Point becomes sexually aroused during a class or meeting in Lincoln Hall his/her erection is called a 'Lincoln Log'.
CDT X: "Have you seen those paintings in Lincoln Hall?"
CDT Y: "Yeah, dude. I go up to the second floor during class sometimes. There's one painting of a naked woman, it totally gives me a Lincoln Log."
CDT X: "Yeah, same. It's so sick when the instructors forget to lock the doors to Lincoln Hall. I can't tell you how many times I've gone in there and beat Navy."