Under criminal law, that is exactly what it means. A defendant's silence may not be used against him in any way. Standard jury instructions include language similar to the following:
Do not consider, for any reason at all, the fact that the defendant did not testify. Do not discuss that fact during your deliberations or let it influence your decision in any way.
I don’t practice criminal defense or con law. However, I think there is a conflict on the issue of using silence as evidence of guilt, which is why the matter is before the Supreme Court.
My discussion is based on my perception of the rationale for the 5th Amendment. We don’t force people to take the stand in their defense, because it seems wrong to do so. We DO allow defendants to testify. It seems fair to me to allow the fact that the Defendant elected not to testify to be argued. The defendant was still not forced to testify.
This only matters if we are trying to determine the truth.