Full stop is a punctuation mark, known as period in North American English, most often used to mark the end of a declarative sentence. It is also used after many abbreviations, to indicate omitted words in a series, and in some regions as a decimal separator. Because it is the most common punctuation mark in texts, it plays a central role in how written language is organized.
Ancient origins
The mark traces back to a system of dots introduced by the scholar Aristophanes of Byzantium in Alexandria in the 3rd century BCE. Different dot positions signaled breaks of different lengths within a thought. Over time scribes mostly kept the terminal dot, and from the 9th century onwards it was written low on the baseline, a form that became universal once printing spread in Western Europe.
Terminology and modern use
British and American writers have long used the terms full stop and period, with full point also common among printers. Usage guides differ on abbreviations and initialisms, and the practice of omitting full stops in acronyms is increasingly common. In British English the dot is also used in times of day, while American and Canadian English usually prefer colons.