The correct answer is A, The official date that the investor formally owns the securities purchased. The settlement date is the date on which the securities transaction is completed—meaning the buyer pays for the securities and the seller delivers them. It is at this point that legal ownership transfers from seller to buyer.

For most equity trades, settlement currently occurs on a T+1 basis (trade date plus one business day), though historically it was T+2. This is an important concept tested on the SIE exam because it impacts when payment is due and when ownership rights begin.

Choice B describes the trade date, which is when the order is executed, not settled. Choice C is incorrect because there is no such general rule allowing cancellation of trades after execution. Once a trade is executed, it is binding. Choice D refers to Regulation T payment rules, which deal with when a broker-dealer must act if a customer fails to pay, not the definition of settlement.

Understanding the distinction between trade date and settlement date is critical, as many regulatory requirements, such as payment deadlines and ownership rights, are tied to the settlement date.