The AT89C2051 is a low-voltage, high-performance CMOS 8-bit microcontroller featuring 2K bytes of flash memory, compatibility with the MCS-51 instruction set, and a variety of integrated components such as timers, interrupt sources, and I/O lines. It operates in both idle and power-down modes to conserve energy, and programming involves a specific sequence for loading and verifying data. Additional features include programmable lock bits for memory protection and multiple pin configurations for versatile applications.