A more thorough explanation:

Definition: A plea not pure is a type of plea that is considered anomalous. It falls under the category of plea of confession and avoidance.

Example: If a defendant is charged with theft, they may enter a plea not pure by admitting to taking the item but claiming they believed it was theirs or that they had permission to take it.

This type of plea is not a complete denial of guilt, but rather an attempt to justify or excuse the actions that led to the charge. The defendant is essentially confessing to the act but avoiding full responsibility for it.