VHDL is a hardware description language used to model and design digital circuits and systems. It allows designers to specify the behavior of a circuit and simulate its operation before it is physically implemented. VHDL is used in the design of field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), and other digital logic circuits. Proficiency in VHDL is necessary for digital design engineers, FPGA designers, and ASIC designers.