Long one put option with a lower strike price and long one call option at a higher strike price.
Risk / Reward
Maximum Loss: Limited to the total premium paid for the call and put options.
Maximum Gain: Unlimited as the market moves in either direction.
When to use: When you are bullish on volatility but are unsure of market direction....
A long strangle is similar to a straddle except the strike prices are further apart, which lowers the cost of putting on the spread but also widens the gap needed for the market to rise/fall beyond in order to be profitable.
Like long straddles, buying strangles is best when implied volatility is low or you expect a large movement of market price in either direction.