/ˈælɡərɪðəm/
[noun] A set of step-by-step instructions or rules that a computer or person follows to solve a problem or complete a task. Algorithms are used in mathematics, computer science, and everyday life to get from a question to an answer in an organised way.
The word 'algorithm' is actually the Latinised name of a 9th-century Persian mathematician — his name literally became the word.
The story of 'algorithm' begins not with a concept but with a person. Around 820 CE, a scholar named Muḥammad ibn Mūsā al-Khwārizmī worked at the House of Wisdom in Baghdad, one of the greatest centres of learning the world has ever known. He wrote a landmark mathematical treatise introducing the decimal number system and systematic methods for solving equations. His name, al-Khwārizmī, meant simply 'the man from Khwarazm', a region in what is now Uzbekistan. It is one of the most remarkable facts in the history of language that this man's geographical nickname would, over a thousand years later, be spoken billions of times a day by people who have never heard of him.
When al-Khwārizmī's works were translated into Latin in 12th-century Europe, his name was rendered phonetically as Algoritmi or Algorismus. Medieval European scholars, encountering the decimal positional number system for the first time, associated the name with the method itself. So 'algorismus' came to mean the practice of arithmetic using the Hindu-Arabic numeral system — the kind of counting and calculating that we now take entirely for granted. The word travelled through Medieval Latin as algorismus, then into Old French as algorisme, before arriving in Middle English as augrim or algorisme, referring to arithmetic and the use of Arabic numerals.
For several centuries, 'algorithm' and its variant forms referred specifically to the process of doing arithmetic with digits — a meaning that seems almost laughably narrow compared to how we use the word today. The modern, broader sense of a defined sequence of logical steps for solving any kind of problem emerged much later, propelled by the rise of formal mathematics in the 19th and early 20th centuries. Mathematicians like Ada Lovelace and Charles Babbage, working on mechanical computation, needed precise language for describing repeatable computational procedures, and the old word was repurposed beautifully.
The spelling 'algorithm' — with the 'th' — came about through a blend of the Latin algorismus and the Greek word arithmos, meaning 'number', which also gives us 'arithmetic' (via Latin arithmetica from Greek arithmētikē). This cross-contamination between two roots produced a hybrid spelling that looks Greek but is, at its heart, Arabic. The '-rithm' ending made the word feel at home beside 'arithmetic', lending it a scholarly respectability that helped it survive into the modern era.
In the 20th century, with the arrival of digital computers, 'algorithm' exploded in importance. Computer scientists adopted it as the precise term for any finite, unambiguous set of instructions that transforms an input into an output. Alan Turing's theoretical work in the 1930s and 1940s gave the concept mathematical rigour, and by the second half of the century, the word had moved far beyond academic papers. Today it sits at the heart of everyday conversation — people speak of social media algorithms shaping their news, search algorithms deciding what they find online, and recommendation algorithms choosing their next favourite film. A medieval Persian scholar's surname has become one of the defining words of the digital age.