Blue chip is a descriptive label rather than a defined category. It generally means a large-cap or mega-cap with decades of profits, an investment-grade balance sheet, and a dividend that has been maintained through recessions. Index membership and deep liquidity come with the territory.
The label is not a guarantee. Companies lose blue-chip status when an industry changes, and several former blue chips have cut dividends or filed for chapter-11 within a decade of being described that way.
Example: a company that has paid an uninterrupted dividend for 45 years, carries an A credit rating, and trades 8M shares a day fits the description; the description does not stop the stock falling 40% in a bear market.
Related: large-cap, dividend-aristocrat, defensive-stock, dividend