Toasty means warm in a pleasant, cosy way — the warmth you want, not the heat you are suffering from. A room with the heating on is toasty. Your bed on a cold morning is toasty. Feet in thick socks are toasty. The feeling behind the word is comfort and safety: warm enough to relax. It is a friendly, casual word, the kind you say to family, not the kind you write in a report. English speakers often stretch it a little further with 'nice and toasty' or 'toasty warm', which say the same thing twice on purpose because it sounds cosy. It comes from toast: bread warmed by fire. There is a second, rarer use, closer to the bread meaning — food or a smell described as toasty means it has that browned, nutty quality, like coffee or roasted nuts. Coffee people use it a lot. But if a student meets 'toasty', it will almost always be the warm-and-comfortable meaning.