A fully connected multi-layer neural network is called a Multilayer Perceptron (MLP). It has 3 layers including one hidden layer. If it has more than 1 hidden layer, it is called a deep ANN. An MLP is a typical example of a feedforward artificial neural network.
How does it work?
Let us take two perceptrons P1 and P2 and add them both together and smoothen it and you will get a curved decision boundary.