A secondary offering is a sale of securities by someone who purchased the security in a primary offering to a subsequent purchaser. That is, a private investor sells their shares to another private investor. Unlike a primary offering, the issuer is not privy to the transaction, so does not receive the proceeds of the sale.
A security-holder may be restricted on selling their security in a secondary offering, depending on the method of the primary offering. If the primary offering was public, then the security-holder may freely resell their security in a secondary offering. If the primary offering was conducted through a private placement, then the seller may not resell the security unless they satisfy Rule 144, Rule 144A, or Section 4(a)(7) of the Securities Act.
[Last updated in January of 2022 by the Wex Definitions Team]