sentence-end

sentence-end is a variable defined in `paragraphs.el'.
Its value is

nil

• This variable is safe as a file local variable if its value
  satisfies the predicate `string-or-null-p'.

Documentation:
Regexp describing the end of a sentence.
The value includes the whitespace following the sentence.
All paragraph boundaries also end sentences, regardless.

The value nil means to use the default value defined by the
function `sentence-end'. You should always use this function
to obtain the value of this variable.

You can customize this variable.