Fund Settlement refers to the transfer of funds from the Buyer of a Stock to the Seller of a Stock. It is also a term used in funds transfers and in that context represents when the funds arrive at the receiving bank from the sending bank.
Stock trades settle 2 business days following the trade date (T+2). So, for two days after the sale of a security, the funds are considered “Unsettled”. Bear in mind the rules regarding trading on unsettled funds to avoid potential restrictions on your account.