What does this mean solid heterogeneous well circumscribed nodule within the right lobe of the thyroid. ?

Nodule: The nodule is not likely to be a cancer but that won't be known properly until a biopsy of nodule is done. If there is no cancer but the nodule is large it is probably best to have removed. Usually straightforward surgery with quick recovery.

Appearance of nodule: Unfortuantely, one cannot clearly determine the cause by the appearance: Solid= not fluid filled like a cyst. Heterogeneous: not uniform in texture. Well circumscribed: sharp margins and not growing into the thyroid tissue. Depending on whether there are multiple or only a single nodule and the size, a biopsy may be recommended to determine the cause, benign or otherwise.