TeX/edef

Description
is similar to \def in that it allows you to define new macros or replace an existing macro. The significant defining difference between  and \def is that   expands macros at definition time, rather than saving them for later. This difference allows  to be used to append new information to a macro, for example: results in the output "ABC". Attempting to do this example with \def instead will result in the error "TeX capacity exceeded, sorry". This behavior can be useful in loops that compile a string of information, but do not end up outputting the information directly.