Das

Das is a German word with several grammatical functions. It is most commonly the neuter definite article used with singular neuter nouns in the nominative and accusative cases, as in das Haus (the house).

Das is also a demonstrative pronoun meaning "that" or "this" when referring to a neuter noun or to a clause, as in Das ist mein Buch (That is my book). It can also function as a relative pronoun introducing a relative clause, as in das Buch, das ich lese (the book that I am reading).

A key orthographic distinction is between das and dass: dass is the conjunction meaning "that" in English and is spelled with double s, used to join clauses, whereas das serves as an article or pronoun and is not a conjunction.

Spelling and capitalization: das is lowercase except at the start of a sentence; when used as a demonstrative or article, it does not carry capitalization within a sentence. Learners commonly confuse the two spellings due to their similar pronunciation.

Beyond German usage, DAS (uppercase) is a common acronym in various fields. Examples include Distributed Acoustic Sensing in fiber-optic systems and Data Acquisition System in engineering contexts. The exact meaning of an acronym DAS depends on the domain and accompanying terminology.

In summary, das is a versatile element of German grammar, functioning as a definite article, a demonstrative pronoun, and a relative pronoun, with a distinct and separate usage from the conjunction dass.