A more thorough explanation:

IN SIMILI MATERIA

in simili materia (in sim-ə-lI mə-teer-ee-ə), adv. & adj.
[Law Latin] Of the same or a similar subject matter.

In simili materia is a Latin term used in law to describe a situation where two legal cases or issues are similar or related to each other. It means that the subject matter of the cases is the same or similar.

For example, if a court is deciding a case about a car accident, and another case comes up that is also about a car accident, the court might say that the two cases are in simili materia. This means that the subject matter of both cases is the same or similar, and the court can use the decision from the first case to help decide the second case.

Another example could be if a lawyer is arguing a case about a breach of contract, and they want to use a previous case as a precedent. If the previous case is about a similar type of contract, the lawyer might argue that the two cases are in simili materia, and the court should follow the decision from the previous case.

These examples illustrate how the term in simili materia is used in law to describe cases or issues that are related to each other because they have the same or similar subject matter.