What does AF mean in beer?

Excuse me, I'm curious about something I've seen in the world of beer. Could you please clarify for me what the acronym 'AF' stands for when it's used in relation to beer? I've heard it mentioned in conversations about different brews, but I'm not entirely sure what it signifies. Is it perhaps related to a specific brewing technique, a certain style of beer, or perhaps a rating system? I'd appreciate any insight you could offer to help me better understand this term.