The open interest represents the total volume of derivatives contracts (futures and options) that are still open (not settled) on a given underlying.
An open-ended fund, as opposed to a closed-end fund, is a mutual fund which can issue or redeem shares according to the level of subscriptions and redemptions.
Options are financial instruments that give their holders the right but not the obligation:
Option prices depend on the underlying price, the strike, the risk-free rate, the maturity and the expected volatility (implied volatility) of the underlying.
Over the counter (OTC) transactions are bilateral trades which are dealt outside of an organised market. In constrast with exchange trading, where some features aim to standardise transactions and reduce counterparty risk, OTCs are especially appropriate for non-standard transactions.