The high street is the most important street in a small town, where you are likely to find most of the shops. At least that was the traditional arrangement. It is also used to talk about everyday commerce: "Prices in the high street have risen by 5 per cent", "high street fashion" (as opposed to more prestigious and expensive designer fashion), etc.
thank you very much for your reply.i have to do a translation from english into italian but i could't find a suitable translation for "high street" because the dictionary isn't very helpful. a question: can the high streets be those shops belonging to big "department store chains"(i don't know if it is the proper term) such as Marks and Spencer?
thanks a lot!