The activation function is the one who decides whether a neuron should be activated or not by calculating a weighted sum and further adding bias with it. The purpose of the activation function is to introduce non-linearity into the output of a neuron.
Transfer function comes from the name transformation and is used for transformation purposes i.e. from input nodes to the output of a neuron. On the other hand, activation function checks for the output if it meets a certain threshold and either outputs zero or one.
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