Flip Flops

• In the electronics world, a flip-flop is a type of circuit that contains two states and are often used to store state information. By sending a signal to the flip-flop, the state can be changed. In sequential logic, it is the basic element of storage. Flip-flops are used in a number of electronics, including computers and communications equipment.

http://www.computerhope.com/jargon/f/flipflop.htm

• In electronics, a flip-flop or latch is a circuit that has two stable states and can be used to store state information. 

The circuit can be made to change state by signals applied to one or more control inputs and will have one or two outputs. It is the basic storage element in sequential logic. Flip-flops and latches are a fundamental building block of digital electronics systems used in computers, communications, and many other types of systems.

http://en.wikipedia.org/wiki/Flip-flop_(electronics)#Flip-flop_types

• Flip-flops are heavily used for digital data storage and transfer and are commonly used in banks called "registers" for the storage of binary numerical data.

http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/flipflop.html

Flip Flops basics:
•Storage elements for synchronous circuits (what is synchronous?)
•Typical configurations:
•SR (set_reset)
•D
•JK
•T (toggle)
http://www.engr.uky.edu/~elias/lectures/ln_13.pdf