A section refers to a section of text inside the tiddler. This is the text between one heading and another heading (or to the end of the document, in the case of the final section). The name of the section is the title. The level of heading (!, !!, !!!, i.e. heading level 1, 2, 3, etc.) is irrelevant for this purpose. See also [[slice]].

Sections can be transcluded with the tiddler macro. eg: {{{<<tiddler section##SectionStart>>}}} <<tiddler section##SectionStart>>
{{{
!SectionStart
>Some text inside a section
!end
This text is outside the section
}}}