According to the Merriam Webster online, bicycle is:  
  Pronounced: 'bI-si-k&l, -"si- also -"sI-
  Function: noun
  Etymology: French, from bi- + -cycle (as in tricycle) : a vehicle with
  two wheels  tandem, handlebars  for steering, a saddle seat, and
  pedals by which it is propelled.

A set of other adjectives to better describe this amazing simple machine include: Reliable, durable, eco-friendly, healthy, economical and fantastic - simply.

If you are confident about your strong legs and have a sturdy will-power, this simple machine can actually take you and your luggage around the globe, several rounds should you have the desire. Bicycles are recommended as the best and only way to travel in order to properly and fully see any country with a pace that connects you to earth, nature and our beloved environment making travel a much more enjoyable and memorable experience.

Only on the simple bicycle that you actually ride to learn the contour of a country best, since you have to sweat and pedal harder up the hills and coast down them easily, thus you remember them as they actually are. While in a car, only a high hill impresses you, and you have no such accurate remembrance of the country you have driven through as you gain by riding your bicycle.

Before you pick your next bike, make sure you are buying what is suitable for your riding requirement. Do you want it for the city or for a weekend outdoor adventure? Are you driven by speed or by varied terrain? These are but examples of the different types of bikes available.
Road bikes

Remember the semi-circular, turned down handle bars and the very thin tires? These are road racing bikes. They are aerodynamic, stiff and light-weight designed for speed and intense workouts. Mostly, on proper roads and highways, but not for comfort as you tend to curl your back when on them. Because of the thin and light frames and tires, they tend to be expensive and delicate machines.

Mountain bikes

Then came the MTB and everyone became euphoric! These are rugged machines that can take you anywhere, from road to dirt to deserts even and over and rocks and logs. The frame design is rugged and for rough riding, but not for speed and distances. They have more gears especially lower ones, fat and knobby tires for better traction and grip. Suspension system (shock absorbers) are becoming more and more standard.  Advantages are fun and all-terrain use.

Touring bikes

A combination of both above, used for bike travellers who want to spend weeks, months or even years on their bikes travelling from one country to another – and there are lots of them! Endurance and reliability is the name of the game here, only the best components can be used from gears, tires, lights and panniers. These bikes can withstand thousands of kilometres and changing weather without any complaints. The frame and all components are designed with two things in mind: Endurance and comfort

City or Hybrid bikes

These are designed for both paved road and dirt tracks but not a strong candidate for either. They are very popular for commuters and people who live in major cities for their quick handling, versatility as well as comfort and ease to use

Tandem bikes

Two bikes in one: These bikes have their own culture, clubs and supporters. They are extremely specialized and therefore not as popular as any other bike. To travel with the same person on the same bike can definitely be an experience. They are long and heavy and definitely cannot fit in the trunk of any car! Tandems come as mountain, road or even a recumbent-tandem. In general, these bikes are custom design; hand built and can be expensive

Recumbent bikes

Probably the most comfortable design among all bikes; you are sitting down in lounge-style seat with legs extended to reach the pedals. Generally expensive and highly specialized as the case with tandems. There is a growing culture for this style of riding

Cruisers or beach bikes

These have very comfortable frames with upright handle bars. Mostly they come in single speed and foot brakes. They are designed for the comfortable easy ride, “California-style”  afternoon along a beach with the family