In 'She wrote a letter', the verb 'wrote' is transitive and the word 'letter' is the direct object.
在She wrote a letter一句中，动词wrote是及物动词，letter一词是直接宾语。
《牛津词典》
2
This word is a transitive verb. We can use a noun or noun phrase as its direct object.
这是一个及物动词，我们可以用名词或名词性短语直接作其宾语。
3
Expressing an action that is carried from the subject to the object; requiring a direct object to complete meaning. Used of a verb or verb construction.