Definition of that conjunction from the Oxford Advanced Learner's Dictionary

      

    that

     conjunction
    conjunction
    BrE BrE//ðət//
     
    ; NAmE NAmE//ðət//
     
    ; BrE BrE//ðæt//
     
    ; NAmE NAmE//ðæt//
     
     
    jump to other results
  1. 1  used after some verbs, adjectives and nouns to introduce a new part of the sentence She said (that) the story was true. It’s possible (that) he has not received the letter. The fact (that) he’s older than me is not relevant. In spoken and informal written English that is usually left out after reporting verbs and adjectives. It is less often left out after nouns.
  2. 2  so… that… used to express a result She was so tired (that) she couldn’t think straight. In informal English that is often left out.
  3. 3(literary) used for expressing a hope or a wish Oh that I could see him again!
  4. Word Origin Old English thæt, nominative and accusative singular neuter of se ‘the’, of Germanic origin; related to Dutch dat and German das.
See the Oxford Advanced American Dictionary entry: that