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I've been working with numbers in fractional form (e.g. 1/2) and written out (e.g. 0.5). However, the numbers are in binary and I do not know what to call the dot between the zero and five in the written out example. Calling it a decimal point seems to imply that I am working in base 10, but that is not true. Is there a term specific to the binary number system?

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    @MikeHarris by popular demand, I have provided an answer. :)
    – RaceYouAnytime
    Commented Dec 13, 2017 at 20:37
  • Related, possible duplicate: "Is there a word that describes the separation of dollars and cents?",
    – MetaEd
    Commented Dec 13, 2017 at 20:42
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    Also see: "A term for 'radix point' that everyone would understand?" (lots of overlap, but not a duplicate). The term "bicimal point" comes up there.
    – MetaEd
    Commented Dec 13, 2017 at 20:49
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    The dot in “0.5” is called a decimal point, as you have written the number in base 10: the “5” after the point means “five tenths”. Yes, “tenths” because you are using decimal notation. The same number in binary would be written “0.1”, where the dot is a binary point, and the “1” means “one half”. Remember: only the digits 0 and 1 are allowed in binary, “5” makes no sense.
    – Edgar Bonet
    Commented Dec 14, 2017 at 10:35
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    One should note here that the term "binary point" is commonly used when discussing binary floating-point arithmetic for computers.
    – Hot Licks
    Commented Dec 15, 2017 at 4:47

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You can refer to this symbol as a radix point no matter what the base is.

In computer science and mathematics, the word radix can mean the same thing as base or root. The contemporary meaning derives from earlier meanings referring literally to the "roots" of plants, and later to roots in a mathematical sense and other senses.

The OED provides this definition:

Math. and Computing. The base of a scale of numeration or a system of logarithms

In binary, the point can also be referred to as a binary point. Here is an example use from the OED under a different headword (mantissa):

After multiplication has been completed the digit following the binary point must be examined and, if this digit is 0, a corrective shift must be applied to the mantissa together with an adjustment of the exponent.

  • 1960 - M. G. Say et al. Analogue & Digital Computers v. 142

Some people have also used the term bicimal point, a portmanteau of "binary" and "decimal," to describe this symbol. Bicimal is not defined in dictionaries that I checked, but it can be found in use.

A bicimal is the base-two analog of a decimal; it has a bicimal point and bicimal places, and can be terminating or repeating.

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    Why bicimal? why combine the word with decimal? wouldn't that suggest 12?
    – tox123
    Commented Dec 15, 2017 at 1:20
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    Radix point is widely used in technical language: For example, Wikipedia's article about the IEEE double precision aka binary64 floating point format uses the term "radix point". Specifically, that it represents numbers with a floating radix point. (As opposed to a fixed-point representation where e.g. the low 4 bits are implicitly fractional and the high 12 bits are implicitly integer, vs. floating point having some exponent bits to indicate where the radix point goes relative to a mantissa aka significant.)
    – Peter Cordes
    Commented Dec 15, 2017 at 9:47
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    @tox123 That would more likely be a 'dodecimal point'.
    – Linear Christmas
    Commented Dec 15, 2017 at 17:16

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