What is a soliloquy in a drama?

The definition of a soliloquy is "a device often used in drama when a character speaks to himself or herself, relating thoughts and feelings,thereby also sharing them with the audience, giving off the illusion of being a series of unspoken reflections." Sometimes other characters are on the stage, but stay quiet or are shown in a way where the character speaking does not feel that them listening to their soliloquy will affect their hidden feelings or the play.