What are the different types of flip-flops?

Main flip-flop types are: SR (Set-Reset) with S=R=1 being invalid state, JK (eliminates invalid state, J=K=1 toggles output), D (Data) which outputs whatever was at D input on clock edge, and T (Toggle) which toggles output when T=1. D flip-flops are most common in modern design due to simplicity. JK and T can be constructed from D flip-flops. Each type can be positive or negative edge-triggered, and may include asynchronous set/reset inputs.