The stock makes its initial move upwards. This is usually caused by a relatively small number of people that all of the sudden (for a variety of reasons, real or imagined) feel that the price of the stock is cheap so it’s a perfect time to buy. This causes the price to rise.
Wave 2
At this point, enough people who were in the original wave consider the stock overvalued and take profits. This causes the stock to go down. However, the stock will not make it to its previous lows before the stock is considered a bargain again.