I get curious eyes every time I bring this up at conventions, so here’s my take in plain terms: futa refers to a fictional character type most commonly called 'futanari' in Japanese circles, and it usually means a character who combines both traditionally female and male sexual anatomy. In practice that often looks like a character with a feminine body and breasts, but also possessing male genitalia. It’s a staple in certain adult-oriented manga, hentai doujinshi, and fan art, although portrayals vary wildly in tone and intent.
Historically the Japanese word had broader meanings around intersex, but in modern pop-culture usage it’s become a specific erotic trope. That matters because real-world intersex people and trans people are not the same thing as this fantasy — futa is a fictional construct that plays with gender and anatomy for imaginative or fetish reasons. Online communities have whole tag systems and art styles dedicated to it, and you'll see everything from comedic depictions to very explicit erotica.
Personally, I treat it like any other fandom niche: interesting for what it reveals about fantasy and attraction, but something to approach with a bit of critical thinking. Creators use it to explore power dynamics, taboo, or simply novelty, and fans respond for different reasons — curiosity, aesthetic appeal, or erotic interest. I find the mix of fantasy and culture around it fascinating, even if it’s definitely not everyone's cup of tea.