In an equity transaction, margin refers to the loan that a dealer extends to a client to facilitate the purchase of securities. The client pays a portion of the purchase price (the margin requirement), while the dealer provides the remainder as a loan. This enables clients to leverage their investments and potentially enhance returns, albeit with increased risk.

Other options:

Amount paid by a client when using credit to buy securities : Describes the margin requirement but does not fully define margin.

Good-faith deposit to ensure future financial obligations : Refers to initial margin in derivatives trading, not equity transactions.

Interest paid by the client to borrow securities : Refers to short-selling, not buying on margin.