Guidelines are more-so things like don't spam, don't reply in all capitals or red font, etc... Things that aren't necessarily legal terms but make a community harmonious or keeps discussion flowing.
Registration Terms are more things that are legal based: we reserve the right to modify/delete user generated content at our discretion, you provide us an unlimited use of your content, you may not create subsequent accounts once banned, etc...
(Please note I am not a lawyer or providing legal advice or stating the above are legal terms which you can claim, just providing examples. If you have any questions on those, please contact a lawyer in your area for advice.)