2-bolt shoes use a compact cleat pattern that works with Shimano SPD, crankbrothers, and Time ATAC pedal systems. The "2-bolt" refers to the two holes in the shoe sole where the cleat attaches.
The biggest advantage is walkability. The cleat sits recessed into the shoe's tread so it doesn't touch the ground when you walk. This makes 2-bolt shoes ideal for mountain biking, gravel riding, commuting, and touring—any situation where you hop off the bike to navigate terrain, grab coffee, or run errands.
The trade-off is a smaller contact area with the pedal compared to 3-bolt road cleats, meaning slightly less stability for pure road racing. But for most riders outside of competitive road cycling, the everyday versatility and walkability of 2-bolt shoes makes them the practical choice.