A more thorough explanation:

A cert pool is a group of clerks who work in the U.S. Supreme Court. They read petitions for certiorari, which are requests for the Supreme Court to review a lower court's decision. The clerks then write a summary of the facts and issues in the case, and often make a recommendation to the justices about whether or not to grant certiorari.

For example, if someone wants the Supreme Court to review a case about a controversial law, they would file a petition for certiorari. The cert pool clerks would read the petition and write a summary of the case for the justices. They might also recommend that the justices grant certiorari if they think the case is important enough.

However, some people criticize the cert pool. They say that the clerks are inexperienced and might not give enough attention to important cases. Others say that the cert pool doesn't actually make the Supreme Court more efficient, because the clerks still have to spend time summarizing cases that the justices might not be interested in.