Peter F. answered 11/04/21
K-12 American History Teacher; 18 Years' Teaching Experience
Hi Angelique,
To answer your questions: it has to do with which presidential candidate in any given political party ranks the highest in terms of popularity among the voters during the individual U.S. State primary elections that take place in the months leading up to the given political party's convention. Once it is determined that one candidate has won enough states and votes to secure the party's nomination for President, that candidate is determined to be the nominee. However, the candidate is not officially declared the party nominee until they themselves accept the nomination publicly at their own political party's convention.