The decimal separator is a symbol used to mark the border between the integer and the fractional parts of a decimal numeral. This symbol can be a period ("."), as is common in United States and other English-speaking countries, or a comma (","), as in continental Europe and many Arabic-speaking countries (which use a slightly different character ٫ instead).^[1][2][3] Decimal point and decimal comma are also common names for the decimal separator. For example, 9.5 means nine and one half in English speaking countries, while in many European countries, the same number might be written as 9,5 (and ٩٫٥ in an Arabic-speaking country).

For ease of reading, numbers with many digits (e.g. numbers over 999) may be put into groups using a delimiter, such as: comma (,), dot (.), half-space or thin space (" "), space (" "), underscore (_), or apostrophe ('). Example, using thin spaces as separator: 20 000 and 1 000 000 for "twenty thousand" and "one million". To stop confusion, different international organizations have called for using spaces, as the digital group separator: ISO, BIPM, IUPAC, and American Medical Association's (AMA).

In many programming languages, digits can be put into groups, to make code easier to read. Ada, D, Fortran, Go, Haskell, Java, JavaScript, Julia, Kotlin, PHP, Python, Rust, Swift, and V (Vlang) use the underscore (_) character for this purpose. The number seven hundred million shows as "700_000_000". In C++ and Red, they use an apostrophe for digit grouping; "700'000'000" in those languages.

• Arithmetic precision
• Decimal degrees
• Dewey Decimal System

1. ↑ "Compendium of Mathematical Symbols". Math Vault. 2020-03-01. Retrieved 2020-08-22.
2. ↑ Weisstein, Eric W. "Decimal Point". mathworld.wolfram.com. Retrieved 2020-08-22.
3. ↑ "Definition of Decimal Point". www.mathsisfun.com. Retrieved 2020-08-22.