Manual:Hooks/ParserAfterStrip
This hook functions identically to ParserBeforeStrip, except it fires after various non-expandable elements (e.g. <nowiki>, HTML comments, etc.) have been stripped from the text.
As of MW 1.14, the hook was deprecated. From this point there is no difference at all between this and ParserBeforeStrip. The hook was removed altogether in MW 1.36.
If you need to apply transformations to the wiki text after the non-expandable elements have been stripped, then you should investigate the InternalParseBeforeLinks. It is not a direct replacement (there are some restrictions on what you can do) but it should handle the majority of use-cases that genuinely need this specific hook.