The LM7805 is an integrated positive voltage regulator which takes DC current and regulates it down to a nice, stable 5 volts. Features include builtin thermal and short circuit protection to keep the magic smoke sealed safely within. The maximum peak output current is 2.2 amps, and the maximum constant load is 1 amp. The maximum input voltage is 35 volts, making it capable of providing a 5vdc output off of an extremely wide range of input voltages. Note that the input voltage must be 7 volts or greater to produce stable output.

The LM7805 is packaged in a TO-220 case or a D-Pak SMD package. The pinout for either is as follows:

 TO-220        D-PAK
 ----- tab   ----- tab
|  O  |     |-----|
|-----|     |     |
|     |     |_____|
|_____|      | | |
 | | |       1 2 3
 1 2 3    1=Input, 2 and tab=Ground, 3=Output

The only support component needed along with an LM7805 regulator is a small capacitor (.1 microfarad or so, value not critical) between the output and ground, to prevent self-oscillation of the output transistor circuit.

Similar parts with different output voltages:
Number   Output Voltage
LM7806     +6.0 
LM7808     +8.0 
LM7809     +9.0
LM7810    +10.0
LM7812    +12.0
LM7815    +15.0
LM7818    +18.0
LM7824    +24.0