What does legal mail include?

Legal mail refers to correspondence that is considered privileged and confidential, specifically relating to a person's legal issues. This typically includes communications between an inmate and their attorney, which is protected under attorney-client privilege. Such correspondence ensures that the inmate's legal rights are upheld and that confidential information regarding their cases is safely conveyed without interference or the possibility of disclosure to others.

The other options do not fall under the category of legal mail. General correspondence and personal letters from friends do not contain legal communication and are subject to different handling and monitoring by correctional facility staff. Advertisements from legal firms are also not considered legal mail, as they do not pertain to the confidential communication about a specific legal matter involving the inmate. Thus, legal mail specifically encompasses confidential information about legal matters, making this the correct answer.