In London, a Travelcard is a single ticket that lets you ride as much as you like on the Underground, the buses, the trams and most local trains, inside the zones you paid for. The point is the word 'as much as you like' — you do not pay each time. You buy one for a day, or a week, or a month, or a year, and then you just travel. It is usually written with a capital T, because it is the official name Transport for London gave it, not a general English word for any travel ticket. So if you say 'travelcard' in another city, people may guess what you mean, but it is not what their own ticket is called. These days many people in London use an Oyster card or just tap a bank card instead, and those work in a different way — they take money for each trip until you reach a daily top price. So a Travelcard now feels a bit older, and is mostly bought by visitors, by people who travel a lot in one day, or by people who want a weekly or monthly one loaded onto their Oyster card. Older Londoners still say 'travelcard' loosely for almost any season ticket, even when it is not really one.

（倫敦）一日／一週交通通行票；地鐵公車通用票