Under Response Data on the listing pages, what do the column and row names mean?

Columns
Initial: Refers to the initial send or query letter, the first response from the listee.
Follow-up: Refers to responses that occur after the initial send, usually in response to a request for additional materials.
Overall: A combination of Initial and Follow-up, giving a complete picture of all responses.

Rows
Offers: The listee has made an offer to the user, either an offer of representation or publication, depending on the type of listing.
Requests: The listee has requested additional materials (often a full manuscript or additional edits).
Rejected: The listee has not accepted the submission.
Withdrawn: The submission has been withdrawn by the user who submitted it, or the user has not heard back after an extended period of time and assumed a rejection.