From BiblePortal Wikipedia

Hastings' Dictionary of the Bible [1]

RESH . The twentieth letter of the Hebrew alphabet, and as such employed in the 119th Psalm to designate the 20th part, each verse of which begins with this letter.

Holman Bible Dictionary [2]

 Psalm 119:153-160

International Standard Bible Encyclopedia [3]

resh , rāsh ר : The 20th letter of the Hebrew alphabet; transliterated in this Encyclopedia as r . It came also to be used for the number 200. For name, etc., see Alphabet .