Online check-in is a convenient process that allows travelers to confirm their attendance for a flight or event via the internet. This service is typically available through the airline's or event organizer's website or mobile app, enabling users to select their seats, add baggage, and receive boarding passes without needing to visit a physical check-in counter. By using online check-in, passengers can save time at the airport and avoid long lines. Most airlines, such as Delta or American Airlines, offer this feature, which usually opens 24 to 48 hours before departure. It enhances the travel experience by streamlining the check-in process.