A barcode is an optical machine-readable representation of data. Originally, barcodes represented data in the widths (lines) and the spacings of parallel lines, and may be referred to as linear or 1D (1 dimensional) barcodes or symbologies. They also come in patterns of squares, dots, hexagons and other geometric patterns within images termed 2D (2 dimensional) matrix codes or symbologies. Although 2D systems use symbols other than bars, they are generally referred to as barcodes as well.The first use of barcodes was to label railroad cars, but they were not commercially successful until they were used to automate supermarket checkout systems, a task in which they have become almost universal. Their use has spread to many other roles as well, tasks that are generically referred to as Auto ID Data Capture (AIDC). Other systems are attempting to make inroads in the AIDC market, but the simplicity, universality and low cost of barcodes has limited the role of these other systems. It costs about half a United States cent (US$0.005) to implement a barcode compared to passive RFID which still costs about $0.07 to $0.30 per tag.
Barcodes can be read by optical scanners called barcode readers, or scanned from an image by special software. Scanning software for 2D codes is built-in to or available for many mobile phones, and is especially popular in Japan, India & Europe.
條碼或條形碼（barcode）是將寬度不等的多個黑條和空白，按照一定的編碼規則排列，用以表達一組信息的圖形標識符。常見的條碼是由反射率相差很大的黑條（簡稱條）和白條（簡稱空）排成的平行線圖案。條碼可以標出物品的生產國、製造廠家、商品名稱、生產日期、圖書分類號、郵件起止地點、類別、日期等信息，因而在商品流通、圖書管理、郵政管理、銀行系統等許多領域都得到了廣泛的應用。
