A Long Strangle is where you are long one put option with a lower strike price for every one long call option at a higher strike price.
The Max Loss is limited to the total premium paid for the call and put options.
The Max Gain is uncapped 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.