hugo/docs/content/en/methods/site/MainSections.md

title	description	categories	keywords	action
MainSections	Returns a slice of the main section names as defined in the site configuration, falling back to the top level section with the most pages.			related returnType signatures []string SITE.MainSections

Site configuration:

{{< code-toggle file=hugo >}} [params] mainSections = ['books','films'] {{< /code-toggle >}}

Template:

{{ .Site.MainSections }} → [books films]

If params.mainSections is not defined in the site configuration, this method returns a slice with one element---the top level section with the most pages.

With this content structure, the "films" section has the most pages:

content/
├── books/
│   ├── book-1.md
│   └── book-2.md
├── films/
│   ├── film-1.md
│   ├── film-2.md
│   └── film-3.md
└── _index.md

Template:

{{ .Site.MainSections }} → [films]

When creating a theme, instead of hardcoding section names when listing the most relevant pages on the front page, instruct site authors to set params.mainSections in their site configuration.

Then your home template can do something like this:

{{ range where .Site.RegularPages "Section" "in" .Site.MainSections }}
  <h2><a href="{{ .RelPermalink }}">{{ .LinkTitle }}</a></h2>
{{ end }}