They mean the same if you follow HTML5’s definitions:
HTML5’s definition of the link type
nofollow keyword indicates that the link is not endorsed by the original author or publisher of the page, or that the link to the referenced document was included primarily because of a commercial relationship between people affiliated with the two pages.
HTML5 refers to MetaExtensions for the registration of metadata names, which says about the
nofollow value for the
[…] "nofollow" works as the link rel value with the same name.
(This was added by Aleksandersen on 2007-06-30.)
(Note that Google Search doesn’t seem to follow HTML5’s definition, but Google Search also makes no difference between
nofollow as metadata name and as link type.)
However, in HTML 4.01, the definition for the
nofollow value in a
robots element is different (bold emphasis mine):
META element allows HTML authors to tell visiting robots whether a document may be indexed, or used to harvest more links. […]
In the following example a robot should neither index this document, nor analyze it for links.
This seems to be in line with the definition on robotstxt.org, where it says about
Don't confuse this NOFOLLOW with the rel="nofollow" link attribute.
And in the linked FAQ entry it says:
From that description it sounds like it only affects the ranking, and the Google robot may still follow the links and index them. If so, it is different from the robots meta tag NOFOLLOW semantics.
(FWIW, the mentioned description doesn’t seem to make this difference anymore.)
And the Microformats wiki says about
rel="nofollow" under open issues:
Name. nofollow is a bad name.
- overloading. does not mean the same as robots exclusion standards (robots.txt, meta robots) nofollow.