1. To suddenly become visible on something. That cat just appeared on my porch! Is he yours? The rash first appeared on my daughter last night, doctor.
2. To act, typically on television or in a play. Early in her acting career, she appeared on many TV shows. That actress hasn't appeared on stage in years.
appear (up)on something
to arrive and be seen on something. (Upon is more formal and less commonly used than on.) A fly appeared on the sterile bandages. A small bird appeared on our mailbox.