The difference between a primary and a general election in the U.S. lies in their purpose and structure. Primaries are internal party elections where registered party members select their nominees for the general election, determining which candidates will represent them. There are different types of primaries, including open, closed, and semi-closed formats. In contrast, general elections determine which candidate will hold a specific office, open to all voters regardless of party affiliation. The primary election is often seen as critical in shaping the final candidates, heavily influencing the dynamics and outcomes of general elections.