A more thorough explanation:

Definition: Shepardizing a citation means to check how a legal decision has been treated in subsequent cases, so that its value as a precedent can be fully understood. The term comes from the name of a tool called Shepard's Citation Service, which was commonly used in the past to track the treatment of specific decisions.

For example, if a lawyer wants to use a previous court decision to support their argument in a new case, they would Shepardize the citation to make sure that the decision has not been overruled or limited by later cases. This helps the lawyer to make a stronger argument and avoid relying on outdated or incorrect legal authority.

The importance of Shepardizing was highlighted in the trial of O.J. Simpson, when one of the lawyers failed to properly Shepardize a citation and was caught off guard by the opposing counsel's argument that the cited case had been overruled.