The seller has changed many of the terms in the offer that was presented for the sale of a house. This would be described as

An amended offer refers to a revision of the existing offer without significantly changing its core terms. If the seller merely adjusted a few details while maintaining the essence of the original offer, it could be described as an amendment. However, since the question specifies that many terms have changed, this does not apply.

A conditional acceptance indicates agreement to the original offer only under certain stipulations. This implies that the original offer remains valid, which contradicts the situation described, as the seller's changes invalidate the original offer rather than conditionally accept it.

A counteroffer typically extinguishes the original offer rather than allowing it to continue. This choice suggests that both the counteroffer and the original offer could coexist, which is incorrect in standard contractual practices. The act of altering terms indicates that the seller is not accepting the original offer.