What is Aid And Abet?

Legal Definition
To assist someone in committing or encourage someone to commit a crime. Generally, an aider and abettor is criminally liable to the same extent as the principal. Also called "aid or abet" and "counsel and procure."
Illustrative case law
See, e.g. Stoneridge Inv. Partners, LLC, v. Scientific-Atlanta, Inc. 552 U.S. 148 (2008).
See also
Legal Definition
In criminal law. That kind of connection with the commission of a crime which, at common law, rendered the person guilty as a principal in the second degree. It consisted in being present at the time and place, and doing some act to render aid to the actual perpetrator of the crime, though without taking a direct share in its commission. See 4 Bl. Comm. 34; People v. Dole, 122 Cal. 486, 55 Pac. 581, 68 Ain. St Rep. 50; State v. Tally, 102 Ala. 25, 15 South. 722; State v. Jones, 115 Iowa, 113, 88 N. W. 196; State v. Cox, 65 Mo. 29, 33.
-- Black's Law Dictionary