[dredmorbius]

There is an extended syntax for that:

  First Term
  : This is the definition of the first term.

  Second Term
  : This is one definition of the second term.
  : This is another definition of the second term.

<https://www.markdownguide.org/extended-syntax>

[ggm]

How this renders is suboptimal to me. It's like a variant of heading.

I meant

  -a        the minus aflag text
  -b        the minus bflag text
  Something the something text

It's basically table or grid layout without lines.

[oneeyedpigeon]

That's a CSS issue rather than anything to do with markdown or the markup it generates.

[dredmorbius]

This.

Markdown (or other markup languages, lightweight or otherwise) in general specify semantic document structure.

The presentation or layout are defined by the style and/or stylesheet --- CSS in the case of markdown.

That said, the definition list is intended to be something of a header/content block, as defined by the W3C.