Learn English – the English name of ‘Santol’

It's mucus:

the slimy protective secretion of the mucous membranes, consisting mainly of mucin

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:

• Snot (uncountable). This is a term for nasal mucus in its normal liquid form.
• A booger (countable, US usage). This is an American term for a piece of dried nasal mucus.
• A bogey (countable, UK usage). This is the UK counterpart of booger.
• A nose goblin (countable). This means the same thing as booger (although FumbleFingers says it's less common; see the comments for discussion, if you'd like).

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.

In a formal setting, it is best to say something like this (while smiling and extending your hand, if appropriate): "Hello, my name is Joseph Biotech. It is a pleasure to meet you. May I ask your name?" There are unlimited ways to express this, but it is always more polite to introduce yourself before asking for a person's name.