What is "null-subject language"

n. A pro-drop language that may frequently leave out subject pronouns that are implied by verbal conjugations, such as Persian, Hebrew, and many Slavic and Romance languages.

In linguistic typology, a null-subject language is a language whose grammar permits an independent clause to lack an explicit subject; such a clause is then said to have a null subject.

Typically, null-subject languages express person, number, and/or gender agreement with the referent on the verb, rendering a subject noun phrase redundant. In the principles and parameters framework, the null subject is controlled by the pro-drop parameter, which is either on or off for a particular language.

For example, in Italian the subject "she" can be either explicit or implicit:

lit. Maria not wants [to-]eat, "Maria does not want to eat". lit. Subject not wants [to-]eat, "[(S)he] does not want to eat."

The subject "(s)he" of the second sentence is only implied in Italian. English and French, on the other hand, require an explicit subject in this sentence.

Of the thousands of languages in the world, a considerable number are null-subject languages, from a wide diversity of unrelated language families. They include Albanian, Arabic, Basque, Berber, Catalan, Chinese, Estonian, Finnish, Greek, Hebrew, Hindi, Hungarian, Italian, Romanian, Japanese, Korean, Persian, Portuguese, Punjabi, Polish, Serbian and other Slavic languages, Spanish, Tamil and Turkic languages, as well as most languages related to these, and many others still. In fact it is rather non-pro-drop that is an areal feature of Standard Average European including French, German, and English.