Fiance Visas ("K-1 Visas") allows a person outside of the United States who is engaged to a U.S. citizen to enter the United States to get married. The marriage must happen within 90 days of the immigrant entering the U.S. After getting married, you can request a marriage-based green card.
Fiance visas typically take about 5-8 months to process after the initial request.
Eligibility (as stated by USCIS)
You may be eligible to bring your fiancé(e) to the United States on a fiancé(e) visa if you meet the following requirements:
You are a U.S. citizen;
You and your fiancé(e) intend to marry one another within 90 days of your fiancé(e)’s admission to the United States;
You and your fiancé(e) are both legally free to marry ; and
You and your fiancé(e) met each other in person at least once within the 2-year period before you file your petition.