Name for number format used in "Section 3.2.1"

Does that kind of numbering style have a common name or names? To be fair, it is really more of an "identifier" since it certainly not a scalar (one-dimensional) number. It isn't fair to call it a floating point number either.

If I were to hazard two guesses, I would say:

• a document identifier (but that seems so vague)
• a multi-dotted number (silly, yes, but it gets the points across)

So in reality, I've got nothing.

The Chicago Manual of Style calls the actual instantiation of such an identifier a "numbered subhead" or sometimes a "numbered division" or "numbered section." It also points out that this particular style of referencing the various sections is called "multiple numeration." See section 1.55 for more info.

I think "section number" makes sense.

Interestingly, Wikipedia's page on Section Numbers redirects to ISO 2145:

International standard ISO 2145 defines a typographic convention for the "numbering of divisions and subdivisions in written documents". It applies to any kind of document, including manuscripts, books, journal articles, and standards.

So, this standard defines the number format I'm looking for. Great. (Note that to satisfy this standard, only Arabic numerals can be used; letters and roman numerals are outside this particular definition.)

Even though, when we hear the word decimal, we might instinctively think of only one decimal point in a number (as in 3.14159265358979), the format you refer to is called a decimal outline.

In addition to the Wikipedia link just provided, the Purdue OWL uses the same terminology, as shown at the end of this handout. This guideline also uses the term decimal outline.

With that in mind, I'd have no problem with someone referring to the 3.2.1 as a decimal identifier, decimal header, or decimal section ID – certainly not in that context – and I don't see any need to specify multi-, as in multi-dotted number.

You might try numbered multilevel list or outline numbered list.

From Microsoft Word 2010 Complete by Pasewark et al. (p. WD 124):

A multilevel list is a list with two or more levels of bullets or numbering. A numbered multilevel list is sometimes called an outline numbered list.