Flexbox Section 4.5 is titled "Implied Minimum Size of Flex Items" -- however, this term used in the title ("Implied Minimum Size") is never defined and has zero usages in the spec's prose, outside of that title (and footnotes about change history).

Instead, the spec's prose uses a different term, "Automatic Minimum Size", which was introduced in this commit and which seems to refer to the exact same concept. Here's a quote, showing the discrepancy:

4.5. Implied Minimum Size of Flex Items
[...]
In general, the automatic minimum size of a flex item is ...
https://drafts.csswg.org/css-flexbox-1/#min-size-auto

For consistency (and to avoid suggesting that there's an additional vaguely-defined concept in play), the title of this section should probably use the same term that we use in the prose -- i.e. the title needs s/Implied/Automatic/.

The exact same is true of Grid, too, BTW (section 6.6 over there).

6.6. Implied Minimum Size of Grid Items
[...]
The automatic minimum size for a grid item in a given dimension is ...
https://drafts.csswg.org/css-grid-1/#min-size-auto

CC @fantasai @tabatkins