Hybrid or Comfort bikes are popular for many reasons. They are a comfortable, approachable, eco-friendly means of getting out with family and friends, running errands, exercising or commuting to work. They don't pretend to be ultra-fast racers and they aren't overbuilt tanks for the off-road trails. They are the middle—an excellent combination of comfort, efficiency and fun.
Also commonly referred to as "Cross", these bikes are the combination (or cross, or hybrid) of a road bike's large diameter wheels and a mountain bike's comfortable, upright position, flat handlebars and low gearing. It is the larger diameter wheels that make the hybrid the quicker, more efficient choice for riding on the pavement. Within this category, you can find models with wider or skinnier tires, rigid or suspension forks, more or less upright positions and lightweight frames.
In most cases they are nearly identical to a hybrid bike, though they use a mountain bike's smaller diameter, sturdier wheels with generally wider tires. One could also look at them as a mountain bike with smoother, more pavement-oriented tires. The durability of the stronger wheels draws people who have rougher commutes, like to ride on trails or are heavier riders.
Beach bikes, beach cruisers and boardwalk cruisers are all other terms for simple, comfortable bikes designed for casual riding along easy, flat pathways. Most use time-proven coaster brakes and count baskets or a rear rack as their main "feature".