MLP - A multilayer perceptron (MLP) is a network of perceptrons (artificial 
neurons) arranged in a feed-forward-only topology. The feed-forward topology is often a requirement, imposed on a 
neural network due to limitations in the 
learning algorithms used.
 
 
The feed-forward limitation leads to a topological 
layering of the neurons in the network. This, in turn, leads to 
hidden layers, another topological feature of 
MLPs
Generally, while natural brains do organize, geometrically, into layers, they also allow for a great deal of topological 
feedback between layers and through the outside world between inputs and outputs.  For more about these types of organizational features, see the entry here for 
Inward and Outward Propagation.