A security traded in some context other than on a formal exchange such as the NYSE, TSX, AMEX, etc. In general, the reason for which a stock is traded over-the-counter is usually because the company is small, making it unable to meet exchange listing requirements.

In so far as gas is concerned, this represents a firm commitment to buy or sell a uniform quantity of gas in the following trading day (OTC DA contract).

The day ahead product is the most liquid contract across all the gas hubs.