An abbreviation for seasoned equity offering or secondary equity offering; an equity issue by a firm that already has common stock outstanding (i.e., that is already listed), regardless of whether the issue consists of primary or secondary shares. In other words, a firm might have a secondary-secondary offering, where further shares are issued in addition to existing ones, or a secondary-primary offering, where new shares are issued by a firm already listed on an exchange (listed company).

If a secondary issue involves shares sold by existing shareholders, then it is said to be non-dilutive. If it involves new shares, then it is referred to as dilutive. Some secondary issues combine selling shares by existing shareholders and new shares (therefore, they are both non-dilutive and dilutive).

It is also known as a follow-on equity offering.