This (Perl) script displays the definitions of (La)TeX command sequences/macros. Various options allow the selection of the used class as well as package files and other factors that may influence the definition (before/after the preamble, inside an environment, …). The script creates a temporary TeX file which is then compiled using (La)TeX to find the ‘\meaning’ of the command sequence. The result is formatted and presented to the user. Length or number command sequences (dimensions, \char…, count registers, …) are recognized and the contained value is also shown (using \the). Special definitions like protected macros are also recognized and the underlying macros are shown as well. The script will show plain TeX definitions by default. LaTeX and ConTeXt are supported, including flavours (pdf(La)TeX, Lua(La)TeX, Xe(La)TeX, …). The flavour can be selected using a command line option, or via the script name: latexdef will use LaTeX as default, etc.