car amplifier question 2 or 4 ?

I would like to know why the ads say in 2ohm mode
or 4 ohm? Is this about the speakerSubwoofer) one buys?
Please keep it simple. Oh and thank you for the help!
they are telling you what the output power is into a certain load. Many solid state amps will deliver more power into a 4 ohm load than 8, often a doubling of power. but at a certain point the amp is not able to deliver sufficient current and may become thermally or electrically unstable and will shut down or worse, melt down.
What Swamp said............

Thank you for the information.