audio port red light
What does the red light in the audio port indicate?
A cool, often ignored, feature of Macbooks is that their 3.5 mm audio jack is also an optical audio output. Whenever a headset is plugged in, it will turn on optical audio. On an Macbook I used to have, the audio jack broke so that it always though a headset was plugged in, thus that red light would stay on. Your computer should be fine, just select the correct audio output in System Preferences and you probably wont notice the difference.
It means your digital audio out has switched on. You can insert a plastic toothpick in the hole and try and switch it off. The switch should be at the 3 o'clock position and go towards the 6 o'clock position. Some people also have had luck inserting their headphone jack and pulling out a few times. Another recent report was that inserting the headphone jack and turning it in the hole helped.
Blowing hard into the hole has also been reported for a fix.