The liquid carry-on limit refers to the restrictions on carrying liquids, gels, and aerosols in your hand luggage when traveling by air. As of my last knowledge update in September 2021, containers must hold 3.4 ounces (100 milliliters) or less and must be placed in a clear, quart-sized plastic bag. Each passenger is typically allowed one quart-sized bag. This regulation is implemented for aviation security purposes. Always verify with the airline or relevant authorities for any updates or changes to these guidelines before your flight.