What is the difference between public SSL certificates and private SSL certificates?

• Public SSL certificates: Issued by trusted third-party Certificate Authorities (CAs), used for internet environments. They are trusted by default by clients such as browsers, and are mainly used to secure data transmission over public networks.
• Private SSL certificates: Usually issued by private CAs built by enterprises or organizations, and only used in internal network environments. Clients need to manually trust the private CA to recognize the certificates normally. They are mainly used to secure communication between internal systems.