What does a tortuous abdominal aortic aneurysm mean?

With twists/bends: The term "tortuous" simply means: full of twists, turns and bends. In medicine we use this to describe the pathway of veins or arteries. When either veins or arteries "grow" to become varicose veins or aneurysms, not only do they grow in diameter, but also in length. As they grow longer, they start bending and twisting to accommodate and "fit" into the same body.

Not straight: It may or may not be consequential. On the other hand, it may cause decrease in blood flow or have clot in it. So, tortuosity per se is not the key issue. Rather, the associated finding that comes with it.

Tortuous aneurysm: It simply means it does not lay in a straight line. You might also say it follows an erratic path rather than lying, more or less, in a straight line.