The pike position has many names - forward folding, hamstring stretch, and so on - but all describe the same movement pattern. I will stick to pike here. It is a movement that challenges and lengthens your whole posterior chain but most will feel it in their calves and hamstrings. While there are many different variations, the pike always involves your upper body getting closer to your lower body, eventually resting completely on it. It should anyhow look like in the picture below.