Closed Primary: In a closed primary, only voters registered with a given party can vote in that party's primary. States with closed primaries include party affiliation in voter registration so that the state has an official record of what party each voter is registered as.
Closed primaries preserve a party's freedom of association by better ensuring that only bona fide members of the party influence who that party nominates, but critics claim that closed primaries can exacerbate the radicalization that often occurs at the primary stage, when candidates must cater to their party's "base" rather than the political center.
In a few states, independent voters may register with a party on Election Day. However, they must remain registered with that party until they change their affiliation again. A handful of states even allow voters registered with one party to switch their registration at the polls to vote in another party's primary.
Sentence
The great state of North Carolina (North Cackalacky), has closed primaries. Therefore, if you are a registered Democrat you may not vote in the North Carolina's Republican closed primary.