LM2940CT-12 12V 1A LDO (Low Voltage Dropout) Regulator
A low-dropout or LDO regulator is a DC linear voltage regulator which can regulate the output voltage even when the supply voltage is very close to the output voltage.
So for example, if you are charging a lead acid battery and running your 12V device from the battery at the same time, the voltage will creep up to above 14V when the battery is full, which might be outside the acceptable range for your components expecting 12V.
This LDO will keep the output at 12V, for currents under 1A.
It's based on a Texas Instruments chip, but this is a Chinese make, so I probably wouldn't run a space ship with this. But for most cases, it should do the trick.