Classical Arabic

Rāʾ (@r@) — the letter R

In ALA-LC romanization, The Arabic letter Rāʾ is represented by an R.

http://www.readwithtajweed.com/tajweed_letterRa.htm

trilled or tapped r with intermittent opening along the median line of the tongue, closure between the sides of the tongue and palate.

the sides of the tongue make contact with the roof. only the middle front part of the tongue where contact is broken to produce a slight trill.