I'm pretty sure both are the same, but my score is not enough to suggest the shorter one as a synonym to the longer one:
http://wordpress.stackexchange.com/tags/custom-meta-fields/synonymshttps://wordpress.stackexchange.com/tags/custom-meta-fields/synonyms
And while browsing so, I found it funny, that themes/theme is synonym-ed but plugins/plugin still isn't: http://wordpress.stackexchange.com/tags/synonymshttps://wordpress.stackexchange.com/tags/synonyms
