Throughout Icarus Verilog descriptions and source code, I use a variety of terms and acronyms that might be specific to Icarus Verilog, have an Icarus Verilog specific meaning, or just aren't widely known. So here I define these terms. LRM - Language Reference Manual This is a generic acronym, but in the Verilog world we sometimes mean *the* language reference manual, the IEEE1364 standard. PLI - Programming Language Interface This is a C API into Verilog simulators that is defined by the IEEE1364. There are two major interfaces, sometimes called PLI 1 and PLI 2. PLI 2 is also often called VPI. UDP - User Defined Primitive These are objects that Verilog programmers define with the "primitive" keyword. They are truth-table based devices. The syntax for defining them is described in the LRM. VPI - This is the C API that is defined by the Verilog standard, and that Icarus Verilog partially implements. See also PLI. VVM - Verilog Virtual Machine This is the Icarus Verilog runtime that works with the code generator that generates C++. VVP - Verilog Virtual Processor This is the Icarus Verilog runtime that reads in custom code in a form that I call "VVP Assembly". See the vvp/ directory for documentation on that.