74HC595: 8 Bit Shift Register with Output Latch

The 74HC595 is a very handy IC used in many microcontroller projects. You clock in 8 bits of data (like, on/off settings for 8 LEDs) via two lines, and when you toggle a third line, it pops these settings out on 8 outputs on the IC. So you trade 3 valuable lines on your microcontroller for 8 outputs.
This is called 'Shifting data out' of the microcontroller by 'synchronous serial communication'. This is the serial part of the deal, where each bit is 'shifted in' one at a time, then BOOM, they all appear at once (in parallel) on the chips output.
The 'HC595 devices contain an 8-bit serial-in, parallel-out shift register that feeds an 8-bit D-type storage register. The storage register has parallel 3-state outputs. Separate clocks are provided for both the shift and storage register. The shift register has a direct overriding clear (SRCLR) input, serial (SER) input, and serial outputs for cascading. When the output-enable (OE) input is high, the outputs are in the high-impedance state.
Both the shift register clock (SRCLK) and storage register clock (RCLK) are positive-edge triggered. If both clocks are connected together, the shift register always is one clock pulse ahead of the storage register.