Symmetric distribution

In a symmetric distribution, folding the graph at its center makes the two halves line up closely. For example, a normal (bell-shaped) distribution is symmetric, with values equally likely to fall the same distance above or below the center. When a distribution is symmetric with a single peak, the mean and median are about equal, so $\bar{x} \approx \text{median}$ (x-bar, the mean, is roughly the median). Symmetry makes the center a natural summary of the whole distribution.