In phonetics, a nasal can also be called a nasal occlusive or a nasal stop.
These sounds are called nasals because they depend on the air escaping from the nose rather than the mouth when you say them.
When you have a cold and your nose is blocked, these sounds become impossible to say.
Try saying, My mum’s monkey sings, while pinching your nose closed with your fingers.
All of the three English nasals are voiced sounds. Most world languages have some nasals. Does yours?