Compare indirect object.
Direct verb objects are the targets of verb actions. In the sentence ის წერს წერილს - she is writing a letter, the letter (წერილი) is the direct object. Go to Lesson 2 to discover more details about this.
Tschenkeli (1958) 31. Lektion, p. 343ff (object markers, objektive Personalzeichen), p. 372 comparison of direct and indirect object markers.