Spoiler tags are pretty good for hiding quotes to shorten your post. Been doing this recently myself; pretty sure this is what you guys are talking about.
Either removing unneeded content, linking as suggested by DragonSnooz (the link can be copied from the post number at the top right) or indeed by using spoiler tags, though generally that's only necessary for content that doesn't already exist such as e.g. the infamously long DXdiag output.
But just as a reminder to everyone, it's generally good etiquette to keep non-original content to a minimum as it's variously tedious and/or awkward for people to scroll through lengthy quoted text.
