Strike Price: 
This is the price of the underlying asset when the initial investment is made. This determines whether you are "in the money" or "out of the money".

Call Option:
This is the binary option that will expire "in the money" when the underlying asset is above the strike price at expiration. It will expire "out of the money" when the underlying asset is below the strike price at expiration.

Put Option:
This is the binary option that will expire "in the money" when the underlying asset is below the strike price at expiration. It will expire "out of the money" when the underlying asset is above the strike price at expiration.

Underlying Asset:
This is the stock, commodity, currency pair, or index on which you are basing your option. This is the basis for the entire binary option.

Expiration:
This is the point at which the option will either pay, or expire in a loss. This is when the underlying asset must be higher to end in the money on a call option, or lower to end in the money on a put option. This can be one hour, one day, one week, or even one month later than the investment is made.