Customer margin Within the futures industry, financial guarantees required of both buyers and sellers of futures contracts and sellers of options contracts to ensure fulfillment of contract obligations. (en.wikipedia.org)
An amount of money deposited by both buyers and sellers of futures contracts and by sellers of options contracts to ensure performance of the terms of the contract (the making or taking delivery of the commodity or the cancellation of the position by a subsequent offsetting trade). (unitedfutures.com)
The strike price is the price at which the buyer and seller of options agree to exchange the underlying asset such as the S&P 500 index. (fxempire.com)