A short sale of a stock is where the seller actually owns the stock, but does not want to close out the position.
A situation in which a person is both long and short in the same security at the same time in his account, a practice usually employed to defer tax liability on capital gains.
Shorting against the box means short selling securities that you already own. This results in a neutral position where your gains in a stock equal the losses. Investors short against the box in order to delay a taxable event; for example, delaying capital gains until the next year.
A type of short sale where the investor owns other shares of the same company, but does not wish to deliver hem at that time. This is done to lock in a profit but delay the tax consequences to another tax year.
A short sale where the investor owns the security, but does not want to use the shares for delivery, so he borrows them from the brokerage firm. This is usually done to lock in a profit, while delaying the tax consequences to a subsequent year.
A short sale of a security in which the seller still owns a long position on the same security. Thus, the overall position on the security is not closed out. This is done to defer tax liability.