Chaos and Complexity
Chaos deals with systems whose outcomes are extremely sensitive to initial conditions. While they may appear random due to their volatile, exponential dynamics, chaotic systems are nonrandom; their outcomes are generated by deterministic processes, iterations of simple rules.
Complexity deals with systems where "the whole is more than the sum of its parts". Complex systems contain a large number of subunits that interact and are interdependent in different ways. Due to these interactions and feedback loops, complex systems generate randomness, nonlinearity, collective dynamics, and emergent behavior.
Note, the definition of "chaos" in chaos & systems theory differs from the colloquially-used definition as a synonym for disorder or randomness.