What is a 26 inch bike?

Answer 1

For an average sized woman it's entirely possible to find a good fitting bike in either wheel size, so it's more a question of finding the most suited bike.

26" bikes are dominated by the MTB versions. Nothing inherently wrong with that, but they tend to come with wide, knobbly tires, suspension fork and nothing much else, which aren't much use if you're doing casual ridíng in an urban environment. But a MTB kitted out with a rigid fork, slick tires and maybe some fenders will usually make a nimble and rugged urban commuter.

28" is where you find most of the hybrid bikes and pretty much all road bikes. Hybrids tends to be the real workhorses for all-round riding, although not as nippy as a roadified MTB nor as fast as a pure road bike.

Road bikes are fast, and, if you have the stamina surprisingly comfortable for long rides. They tend to suck from the usefulness perspective though. No room for fenders and prone to wheel/tire damage on poor roads

Answer 2

Basically any bike with a wheel size of about 26".

26" bikes are dominated by the MTB versions. Nothing inherently wrong with that, but they tend to come with wide, knobbly tires, suspension fork and nothing much else, which aren't much use if you're doing casual riding in an urban environment. But a MTB kitted out with a rigid fork, slick tires and maybe some fenders will usually make a nimble and rugged urban commuter.