What is vpp in 8051 pin diagram?

In the 8051 microcontroller pin diagram, Vpp refers to the programming voltage pin, which is used during the programming of the microcontroller's memory. It is typically set at a high voltage (around 12V) to enable the programming mode for the internal flash or EPROM. This pin is crucial for writing data into the memory during the initial programming phase and is not used during normal operation.