Ghasts were a subtype of ghouls.
They resembled very closely their undead cousin, except perhaps being just a bit more slender and ghost-like. The stench of death and rot lingered around their undead forms.
Ghasts were also far more deadly and cunning than ghouls, with their paralytic touch dangerously affecting their opponents, especially elves. 
They often laired with others of their own kind or acted as the leaders of a group of normal ghouls.
Like ghouls, ghasts spoke whatever language they did in life.
- ↑ 1.0 1.1 1.2 1.3 1.4 Skip Williams, Jonathan Tweet, Monte Cook (July 2003). Monster Manual 3.5. (Wizards of the Coast), p. 119. ISBN 0-7869-2893-X.