VLSI systems are designed using hardware description languages (HDLs). There are three types of HDLs: VHDL, Verilog, and System Verilog. VHDL and Verilog are considered a general-purpose digital design language, and System Verilog is an enhanced version of Verilog.
These HDLs are not software programming languages but the ones that describe propagation time and signal strengths - in short the behavior of electronic circuits or products. System Verilog combines HDLs and a hardware verification language. It takes an object-oriented programming approach.