Claude Elwood Shannon

1. Information Entropy

The measure of uncertainty or information content in a source.

$$ H(X) = - \sum_{i} P(x_i) \log_2 P(x_i) $$

2. Channel Capacity

The upper bound on the rate of information transmission.

$$ C = B \log_2\left(1 + \frac{S}{N}\right) $$