Ra is the tenth letter of the modern Arabic order and the twentieth of the older abjad order, from which it takes the numeral value two hundred. It is written as a short stroke that begins on the line and curves down below it, undotted. The same stroke marked with one dot above is zay. Ra joins only to the right, so it closes the connected group it stands in.
Its sound varies in a way that matters for recitation. Ra is normally a tapped or trilled r, but it darkens in the environment of the back vowels and of the emphatic consonants, taking on the raised tongue quality that sad, dad, the emphatic ta and za carry inherently. The rules governing when ra is light and when it is heavy are among the first things taught in tajwid, the discipline that regulates Quranic recitation, and they are not recorded by the script.
Ra is a sun letter, so the lam of the definite article assimilates to it. Its name descends from the Northwest Semitic resh, whose sense was head, and it is the cognate of Hebrew resh, Syriac rish and the corresponding Samaritan letter. Ra also stands among the fourteen letters that appear in disjoined form at the head of certain suras of the Quran, where it closes a group of five suras opened by the letters alif, lam and ra.