What does 'deng' mean in Chinese?

There are many characters in Chinese that mean 'deng', but the most common ones would be:

等 Děng "to wait"

燈 Dēng "light (like a lamp)"

登 Dēng "ascend"

All that matters is the tone marks. One change of a tone mark can you give you a totally different character and meaning.

The most likely "deng" you are referring to is the first 等 Děng "to wait". Usually used like: 等等 Děng děng "wait a moment".