What is Sigmoid Function and Explain in detail?

Sigmoid is an activation function which is in S shape curve. It takes real value as an input and gives the output which is in between 0 and 1. It is non-linear in nature; it is continuously differentiable and has fixed output range of values. It gives a continuous form of output unlike Step function. It has smooth gradient. At the ends of the sigmoid function, Y values change less with change in X values, due to which vanishing gradient arises which results in Network refuses to learn further or too slow to make correct Predictions. Sigmoid Function is not zero centered.

A = 1/(1 + e^-x)