What does under offer mean ?

The term under offer and sold subject to the contract are used almost for the same thing. The ask offers the status of the property can depend on the estate agent handling the sale. 

The property can be described as “under offer” if there is an offer made for it but rejected by the sellers as the person expecting to sell the property is yet to make a decision and may ask offers to find the best and final offer.

Most agents will not use the word for such status as it puts off other buyers. This can be applicable when the offer has been accepted, but the asking price can be lower; on the other hand, sold subject to a contract may indicate the offer has been accepted as required by the asking price, but the paperwork is pending.