Question

ɾ "Flapped R". American English t and d are pronounced this way typically between vowels, when the first vowel is stressed: kitty, atom, leader, liter, ladder. This is the sound of Spanish single r when it is not at the beginning of a syllable: pero, bruto, dar.

Accepted Answer

Alveolar Flap http://en.wikipedia.org/wiki/Alveolar_tap

Symbol	ɾ
Name	Alveolar Flap
Notes	"Flapped R". American English t and d are pronounced this way typically between vowels, when the first vowel is stressed: kitty, atom, leader, liter, ladder. This is the sound of Spanish single r when it is not at the beginning of a syllable: pero, bruto, dar.
Ref	http://en.wikipedia.org/wiki/Alveolar_tap

R T D Er ɾ Alveolar Flap Flapped