Everyone carries an Octopus card in Hong Kong, because it’s used everywhere. When you take the bus, you pay the fare by tapping your wallet (with Octopus card in it) on the scanner; the fare may change depending on whether you take it before or after crossing the harbour. Subway fares aren’t flat-rate either, so shorter routes are cheaper. The distance you travel is tracked by scanning your card when you get on and again when you get off, and the appropriate amount is deducted.
Even vending machines, parking meters, convenience stores, and restaurants have Octopus scanners used to pay for their services. It’s also used as an identity system, where students sign-in to class by tapping their cards on door scanners, or residents enter their apartment buildings without needing a key.
The Chinese name for the card is “eight arrived pass”, because eight has special meaning in Chinese, especially when it comes to directions. The English name comes from an octopus having eight tentacles, and the logo is an infinity symbol that’s also in the shape of an eight. So clever.