A ticker is usually shorthand for a ticker symbol, the entry that explains how these identifying codes work for shares, funds, currencies and cryptocurrencies. This page explains the word itself, which has two closely related meanings in markets.
The first meaning is the code. When traders say a coin "trades under the ticker ETH" or ask for a company's ticker, they mean the short combination of letters used to find and quote the asset on an exchange. On crypto sites, the ticker is shown next to each asset's name and in the trading pair, such as BTC/USD for bitcoin against the dollar.
The second meaning is a display of prices. The word comes from the stock ticker, a telegraph machine introduced in the 1860s that printed share prices on a narrow paper tape with a ticking sound. Today, a ticker is the scrolling strip of prices seen on financial television, websites and stock exchange walls, and many crypto exchanges provide a "ticker" data feed through their API, giving the latest price, 24-hour change and trading volume for each market.
Both senses are related to the term symbol, which trading software often uses instead. In crypto, tickers are not unique or controlled by any central body, so different tokens may share one, and users should confirm a token's contract address before trading.