What is the difference between a soliloquy and an aside?

A soliloquy is a speech by a single actor.... the actor is alone and speaks to himself, the audience can hear the soliloquy but it is not directed toward the audience.

An aside is a comment or remark directed toward the audience. They hear what the other characters in the play do not.

A soliloquy :

Solo from Latin means "to oneself" and loquor means "I talk". Soliloquy is often used in drama when a character speaks to him or herself, relating thoughts and feelings. The speaker shares with the audience his thoughts and feelings and/or giving off the illusion of being a series of unspoken reflections while aside is usually a brief comment, rather than a speech that is unheard by the other characters on stage

While both asides and soliloquies consist of a character expressing their inner thoughts to the audience, an aside is shorter than a soliloquy.