Looks like a comment, but isn't.... what is the yellow box called?

[Retail Services]

I'm using a spreadsheet set up by another user and when clicking in cells in
a column, what appear to be comments appear. What are they, and how do I
remove them?

 

[Gaurav]

Check Data>Validation>Input Message

 

[Gary''s Student]

Comments are "activated" by mouse_over. The text that appears from clicking
is probably Data Validation messages. To remove, just click on the cell and
pull-down:

Data > Validation... and use the UI that appears.