An idiolect is the “dialect” of one person. It is unique to that person. We all speak an idiolect unique to us. No one else speaks in exactly the same way as you do. In fact, the varieties of idolects among speakers of even the same dialect can be quite pronounced, to say nothing of speakers who have been acculturated to different dialects.
Virtually, the same thing is true for our use and understanding of semiotics. Each one of us has a unique tangle of semiotics even if we share the same culture. Even if two people were born and raised in the same very strict cult, they will have different takes on their “shared” semiotics; they will see thier semiotics in individual and unique ways.
The term “idiolect” is a blend of the prefix idio, which means “own, personal, distinct to the individual” and the suffix lect, which is taken from the word “dialect.”