means A speech in which a character, alone on stage, voices their private thoughts aloud for the audience to hear.

from Coined from Latin: 'solus' (alone) plus 'loqui' (to speak), so literally 'a speaking alone.' The blended Latin form 'soliloquium' is credited to St. Augustine, who used it as a title for a work imagining a dialogue with his own reason; it entered English in the 17th century and found its natural home in the theatre.