[elefanten]

It refers to the practice of changing the conversation (often towards accusation of hypocrisy) rather than answering a claim. Especially when the comparison is different in kind or scope, or just plain irrelevant.

Making comparisons is valid, but it doesn't make you incapable of responding to the original arguments.

[starbeast]

Often it is used to shut down a line of argument when the comparison is entirely valid though.