The Low Level Hardware Description language is an intermediate representation for digital circuit descriptions, together with an accompanying simulator and SystemVerilog/VHDL compiler.
LLHD separates input languages from EDA tools such as simulators, synthesizers, and placers/routers. This makes writing such tools easier, allows for more rich and complex HDLs, and does not require vendors to agree upon the implementation of a language.
Try it yourself
Edit the SystemVerilog on the left and see how it translates to LLHD on the right.