Refers to density. Hounsfield units are a measure of how easily xrays penetrate the object, and therefore how dense it is. For example structures with lots of air in them, allow xrays to easily pass and have very low hu values ( lung would be (-) 700, water is 0, muscle has a score of 40, bone being very dense is 700. What a score of 61 means depends on other factors ( where the tumor is, its shape etc).
Means not much. Hounsfield units measure the density of the issue making it appear lighter or darker on the ct scan image. It's does not measure malignancy. The latter is determined by the shadow's shape and location. In your case the fact that it was called a "tumor" was from those factors rather than the h. Number itself. Know that eventually, cancer can be diagnosed only on a biopsy seen under a microscope.