what does "burning" mean?

Question

I found this sentence in Cambridge dictionary when looking up the word "relive":

Whenever I smell burning, I relive the final moments of the crash.

Cambridge Dictionary

Then I looked up the word burning in Oxford Advanced Learner's Dictionary and saw these meanings:

1. (of feelings, etc.) very strong; extreme
2. a burning issue/question: a very important and urgent problem one of the burning issues of the day
3. (of pain, etc.) very strong and giving a feeling of burning
4. very hot; looking and feeling very hot
5. burning eyes (literary) eyes that seem to be staring at you very hard

Oxford Advanced Learner's Dictionary 9th edition © Oxford University Press, 2015

And it says that burning is used only before noun when it's an adjective and in the phrase burning hot as an adverb. Here it's not before a noun but after a verb and I don't know which meaning is the one of "burning" in the example.

Answer 1

This is not the adjective, but a noun, and means "fire", or "smoke coming from something that is nearly on fire".

So this means the same as "Whenever I smell smoke...".

It is common to make the phrase "smell burning" since the smell of smoke is often the first warning you have when your dinner is burnt or the house is alight.

Answer 2

Your dictionary examples are of the adjective 'burning'. The word 'burning' in your sentence is a form of the verb 'burn', the gerund, which works as a noun itself, meaning the process that takes place when something burns. It is the direct object of 'smell'.

Answer 3

The word "burning" is a shortened form "something burning".

Something is burning means it is on fire.

So " I smell burning" means "I smell that something is on fire."