Okay, so have you ever heard of India? It’s a really big country with lots of different states inside of it, and one of those states is called Tamil Nadu. The people who live in Tamil Nadu are called Tamils, and some of them might also call themselves Madrassis.
“Madrassi” is actually a nickname for people who live in the city of Madras, which is the old name for Chennai, the capital of Tamil Nadu. Sometimes people use the term “Madrassi” to refer to all Tamil people, but this isn’t really accurate.
So basically, if you meet someone who calls themselves a Madrassi, it just means they’re from Chennai or Tamil Nadu, and they might speak the Tamil language. It’s kind of like how someone from New York might call themselves a New Yorker, or someone from Texas might call themselves a Texan. It’s just a way to identify where you’re from!