A loud, emphatic, exclamation of extreme emotion, usually horror, fear, excitement et cetera. Can be the exclamation of a word, but is usually a sustained, high-pitched vowel sound, particularly /æ/ or /i/, in any case, the loudest and most emphatic sound a human can make tends to be a scream. The term is not generally applied to sounds made by non-humans.
The woman across the street testified that the moment after she saw the killing, that is, a moment after the train went by, she screamed, and then went to telephone the police.