Options contracts with stocks as the underlying asset. Options contracts are securities that grants the buyer the power but not the obligation to buy or sell the underlying asset at an agreed price.
There are 2 types of stock options; Call Options and Put Options. Call options allows the buyer of the option to buy the stocks from the seller at the agreed price anytime before expiration and Put options allows the buyer of the option to sell the stocks to the seller of the option at the agreed price anytime before expiration.
When you buy or own a stock option, you own the rights to make the seller of the option perform the contract whenever you want to, only when you want to. Hence the term "no obligation". When you buy a call option, you can demand the seller to sell you the stocks at the agreed price even if the stock is actually at a much higher price. When you buy a put option, you can demand the seller to buy your stocks at the agreed price even if the stock is much lower.