HDL is an acronym that stands for Hardware Description Language. The acronym itself captures the entire theme of the language. It also describes the hardware in the same manner as the schematic.
VHDL stands for VHSIC Hardware Description Language. VHSIC stands for Very High Speed Integrated Circuits. VHDL is being used for the documentation, verification, and synthesis of large digital designs. This key feature of the VHDL saves a lot of design effort since the same VHDL code can theoretically achieve all three of these goals. In addition to being used for each of these purposes. VHDL can also be used in three different approaches for describing the hardware. These three different approaches are the data flow, and structural and behavioral methods of hardware description. A mixture of those three methods can also be employed to arrive at an efficient design.