There are multiple definitions - click on the translation that matches your context.
a person who formally applies for a job or position etc
The company refuses to release the applicant's name.
a person who makes a formal request for something
The applicant submitted her request under the Freedom of Information Act.
a person who makes a request for a case to be heard by a court, especially an appeal from a lower court
The applicant could successfully petition the Supreme Court for permission to appeal.