The name lparse is derived from xparse. The ‘x’ has been replaced by an ‘l’ because this package only works with LuaTeX. ‘l’ stands for “Lua”. Just as with xparse, it is possible to use a special syntax consisting of single letters to express the arguments of a macro. However, lparse is able to read arguments regardless of the macro system used — whether LaTeX, or ConTeXt, or even plain TeX. Of course, LuaTeX must always be used as the engine.