What does hypoattenuating mean as a characterization of an observed area on the liver?

It generally means: it is of lower density than normal liver tissue. For example, a liver cyst, containing fluid, would be hypoattenuating compared to solid liver tissue. In your case, there is not enough information provided to assess whether it is a significant finding or not. Benign things can be hypattenuating, and more serious things can be hypoattenuating. Would need to see report and/or images.