A section is a military sub-subunit. It usually consists of between 6 and 20 personnel. NATO and U.S. doctrine define a section as an organization "larger than a squad, but smaller than a platoon". As such, two or more sections usually make up an army platoon or an air force flight.

In the Australian, British and Canadian Armed Forces section is an equivalent to an infantry squad:

In this regard, in a number of Slavic languages the morphological equivalent of the word "section" (a separate part of an organization; Belarusian: аддзяленне, Bulgarian: отделение, Russian: отделение, Rusyn: удділеня, Ukrainian: відділення) in military affairs also means squad.

At the same time, in a number of Romance languages the phonetic analogue of the word "section" (French: section, Spanish: sección, Romanian: secţie, Italian: sezione) in military affairs means platoon or a sub-unit similar to a platoon.

In some air forces, a section is a unit containing three to four aircraft (if it is a flying unit) and up to 20 personnel. In the U.S. Space Force two or more guardians form a section.

U.S. Army in Chapter 2 of Army Doctrine Publication No. 3-90 provides the following definitions for army echelons:

U.S. Army Field Manual No. 1-02.2 in Table 2-3 and NATO standard APP-06 in Table 1-8 provide the following symbols for these echelons:

In practice, the meaning of these symbols depends on the NATO member country. For example