Double top: It appears as two consecutive tops of around same height and at similar price and the difference between of two peaks is called a valley. When the pattern falls below the neckline, this indicates a start of trend of fall in price until it settles at a new neckline. However, if the price rises from the neckline again, then it specifies reaching a new top thus forming a triple top pattern, after which the prices will fall below neckline.
Double bottom: This specifies the end of a declining pattern and beginning of uptrend in the market. The pattern has two bottom points and one peak and the difference between bottoms is called a valley. After the second bottom, the rise in stock price starts.