Top-notch means the very best in quality — as good as that kind of thing gets. You use it for work, service, food, equipment, a player, a school, almost anything that can be judged as good or bad: 'top-notch service', 'a top-notch chef', 'top-notch equipment'. It is an informal, friendly, spoken word. It is the kind of praise you give happily and quickly, not the kind that goes in a serious report or a contract. Because it is warm and casual, it sounds a little bigger than the plain word 'excellent' — when someone says a meal was top-notch, you hear that they enjoyed it, not just that it met a standard. A 'notch' is a small cut mark, the kind you cut into a stick to count something; the top notch is the highest mark on the stick, so top-notch is 'as high as the marks go'. It sits before a noun most of the time ('a top-notch team'), but it is also fine after 'be' ('the food was top-notch'). It has no comparative form that sounds natural — people do not really say 'more top-notch'; the word already means you have reached the top. Note also that older speakers use it more freely than young ones, who might reach for 'amazing' or 'insane' instead, so it can sound slightly like a teacher's or a parent's word.