When buying a house, "under offer" means that a tentative agreement has been reached between the buyer and seller, but no official documents have been signed. At this stage of the buying process, either side can pull out of the deal without legal repercussions.
If a house remains "under offer" for a significant length of time, new offers can be made by other potential buyers. For the buyer who verbally agrees to buy the house from the seller, time of is of utmost importance. To finalize a deal, the buyer must either release the funds or secure a mortgage. A valuation must be performed to determine the details of the loan, and it is also advised that the buyer order an extensive survey of the property's condition.