Mountain bikes come in many different forms. Two main differences between them are full suspension frames and hardtail frames. Full suspension meaning there is a shock absorber in the front and the rear. Hardtail meaning there is no rear shock absorber. A bike with full suspension is going to favor a rider who is looking to ride steep, rocky trails or lift access bike parks such as Whistler or Sun Peaks (Slash, Top Fuel, Fuel EX). Hardtail bikes are going to be better for cross-country and leisure riding (Marlin, Roscoe, Procaliber).
Often called drop bar bikes, road bikes have many different categories within itself. The main categories within road bikes are race, endurance, gravel, and triathlon. Race and triathlon bikes can be distinguished by their aggressive geometry, aerodynamic frames, and narrow tires (Emonda, Madone, Speed Concept). Endurance bikes will have a more relaxed frame design, allowing for longer rides and added comfort (Domane). Some endurance bikes will have the same capabilities as gravel bikes with the option to add fenders and wider tires. Gravel bikes will fall in between a light duty mountain bike and an endurance road bike. Gravel bikes have lots of tire clearance and mounts for bags for bike packing (Checkpoint, Search).
Hybrid bikes, or "commuter bikes" are very versatile. Most hybrid bikes will be able to be ridden on a variety of surfaces from rough gravel trails to quiet side streets. Off-road hybrid bikes will have wider tires than most and sometimes have a shock absorber like a mountain bike (Dual Sport). Road hybrid bikes or commuter bikes more closely resemble a road bike. The main difference being hybrid bikes have a flat bar, apposed to a drop bar. Similar to road bikes, they have narrower tires, endurance geometry, and a wide range of gears. This type of bike can be used for commuting, fitness, or leisure riding (FX, Verve). Both options will have the ability to mount fenders, lights, and many other accessories.