The main difference between a monologue and a dialogue is that the first one is a speech performed by a single character, while the second one is a conversation between two or more characters.
The monologue is a one-sided conversation in which a person addresses a specific audience. An example of monologue can be found in Claudio's monologue in Shakespeare´s play measure for measure.
The dialogue is an exchange of words between two or more people. There are many different kinds of dialogues according to the situation and the people involved, such as moral, structural, etc.
