"turnover" is typically used by european and asian companies instead of "sales" or "revenue" but they mean the exact same thing. Turnover can also be used to describe certain types of financial metrics for balance sheet line items (inventory turnover, AR turnover, etc).

Sales is related with the commodity/item which come either under CST and VAT and return is being filed in periodic basis. But, when we talk about turnover, it consist of sales as well as services, amc and other related income petaining to main business of firm/company. Rest are included in other income or misc. income.