BB86 is a press-fit bottom bracket standard with a 41mm shell diameter, and you'll find it most often on carbon frames from major manufacturers. It's designed around Shimano's 24mm crank spindle, so crank compatibility is straightforward if you're running Shimano or similar setups. The wider shell allows frame builders to create a stiffer bottom bracket area, which translates to efficient power transfer when you're grinding up loose climbs.
The trade-off is that BB86 shares the same potential downside as other press-fit standards: it can creak over time, especially with the mud, water, and grit that gravel riding throws at it. The bearings press directly into the frame shell rather than threading in, so removal and maintenance require specific tools and more effort than a threaded setup.
If you're comparing gravel bikes and see BB86, it's not a dealbreaker — just plan on keeping the area clean and using quality installation paste. If low-maintenance ownership is a priority, you may prefer a threaded option like BSA or T47 instead.