Regex macro to remove only lines NOT containing specific content

Question

Given a word list, I would like to delete all lines that do not have a specific content.

For illustration, In the following list, I would like to delete all lines that do not end in s.

bird
chairs
dogs
cars
cat
elephant
elephants

After running the macro, the new list should be

chairs
dogs
cars
elephants

Does it matter that I am looking for a single character? If it does, then delete lines not ending in rs which would yield the following new list.

chairs
cars

Answer 1

As BLayer mentions, the idiom here is

:vglobal/pat/delete

Shorthand :v/pat/d. :vglobal (or :global!) acts on lines not matching the pattern, where as :global/:g acts on lines matching the pattern.