a second (or subsequent) action to increase the effectiveness of an initial action. Also used attributively;
as a follow-up visit.
"A follow-up may be of various types. After a medical examination, a second examination (or reexamination) to obtain additional information regarding some fact discovered in the first examination is considered a follow-up. A second visit or phone call in pursuit of a sale or other request would also be a follow-up."
[WordNet 1.5]