I had caught fever and and my nose was running. I want to know that what to call the stuff that comes out of a running nose, in English. In Hindi, we say "Naak".
You have mucous membranes in places besides your nose, though, so if you need to be specific you can refer to it as nasal mucus. You can also refer to it as nasal discharge, meaning a substance coming out of your nose.
There are a number of informal terms for mucus, most of which sound quite childish. Nonetheless, I'll list them:
Of these, I think snot is the most acceptable when used by an adult, but they're all rather informal. If you're talking to a doctor, nasal mucus or nasal discharge would be fine.
If you're just describing liquid coming out of your nose, but you don't want to use medical-sounding terms like nasal discharge, then you can say your nose is running or that you have a runny nose.
The medical term is mucus, but a common informal word is snot: