With Democratic U.S. presidential hopefuls Barack Obama and Hillary Clinton locked in a tight battle for delegates needed to win their party's nomination, much attention is being put on the role of so-called "superdelegates."

Candidates in Democratic Party primaries and caucuses are allotted delegates based on their performance in the popular vote.

However, about 800 delegates, or 20 percent of the total number of delegates at the party nominating convention in August, are superdelegates. They could play a major role in deciding who wins the party's nomination.

Superdelegates are Democrats elected to public office, like governors and members of Congress, as well as senior party members. Superdelegates were created so that senior party members and veteran lawmakers of the Democratic Party would have a role in the nominating process.

But critics of the system say superdelegates can overturn the wishes of voters by tipping the nomination to one candidate, even if the other gets more votes in state primaries and caucuses.

Although some superdelegates already have committed to either Clinton or Obama, many remain undecided and have become the subject of intense political pressure from both campaigns.