A barcode (also bar code) is a visible, machine-readable interpretation of data depicting the thing that bears the barcode. Traditional barcodes consistently convey meaningful data, by altering the widths of and spacing between, parallel lines. As such it may be referred to as linear or one-dimensional (1D) representation of data. Later, two-dimensional (2D) variants were developed, using rectangles, dots, hexagons and other geometric patterns, called matrix codes or 2D barcodes, although they do not use bars at all. Initially, barcodes were only scanned by special optical scanners called barcode readers. Later application software became available for devices that could read images, such as smartphones with cameras.

Norman Joseph Woodland and Bernard Silver invented the barcode and patented in the US in 1952. The invention was based on Morse code that was extended to thin and thick bars. However, it took over twenty years before this invention became commercially successful. 

Barcodes became economically fruitful when they were used to automate retail store checkout systems, a task for which they have become almost universal. Their use has spread to many other tasks that are generically referred to as automatic identification and data capture (AIDC). The now-ever-present Universal Product Code (UPC) barcode was scanned on a pack of Wrigley Company chewing gum in June 1974.[4] QR codes, a specific type of 2D barcode, have recently become very popular.

Barcodes such as the UPC have become a ubiquitous element of modern civilization, as evidenced by their enthusiastic adoption by stores around the world; most items other than fresh produce from a grocery store now have UPC barcodes.[citation needed] This helps track items and also reduces instances of shoplifting involving price tag swapping, although shoplifters can now print their own barcodes.[17] In addition, retail chain membership cards (issued mostly by grocery stores and specialty "big box" retail stores such as sporting equipment, office supply, or pet stores) use barcodes to uniquely identify consumers, allowing for customized marketing and greater understanding of individual consumer shopping patterns. At the point of sale, shoppers can get product discounts or special marketing offers through the address or e-mail address provided at registration.

They are widely used in the healthcare and hospital settings, ranging from patient identification (to access patient data, including medical history, drug allergies, etc.) to creating SOAP Notes.

They can also be used to keep track of objects and people; they are used to keep track of rental cars, airline luggage, nuclear waste, registered mail, express mail and parcels. Barcoded tickets allow the holder to enter sports arenas, cinemas, theatres, fairgrounds, and transportation, and are used to record the arrival and departure of vehicles from rental facilities etc. This can allow proprietors to identify duplicate or fraudulent tickets more easily. Barcodes are widely used in shop floor control applications software where employees can scan work orders and track the time spent on a job.