What is the difference between the
\def commands in TeX/LaTeX?
Ideally please provide a simple example that will illustrate the difference between them.
The difference is in the time at which the 'right hand side' is evaluated.
On the other hand,
While the existing answers are all true I like to highlight one point which wasn't explicitly mentioned yet. I myself got this information recently from Joseph Wright (see his answer and our comments in Simple un-obfuscation of some LaTeX internals).
As Michael said
They're pretty completely different.
creates a new command
copies the commands from the