The term martial arts encompasses a vast set of fighting styles but generally most center on the systems coming from the orient. This type of fighting is markedly different than the western styles of fighting which involved boxing, wrestling and western style weaponry.
Asian styles often have a stylized format, salutation forms, are meant to develop mind and spirit, and often have sets of codified conduct and rules. These styles involve using all parts of the body in striking and in defense such as the feet, knees, hands, elbows and more. Throwing, evasion, submissions locks and pressure points are also inherent to the Asian styles as opposed to western fighting.
Styles developed based on the regions they came from. For example Karate is from Japan, Taekwondo is from Korea, Kung Fu would be from China, and Muay Thai would be from Thailand. Today in America there is a wide diversity of fighting systems and many of them are even merging. The term mixed martial arts involves drawing out strong points from several style and making them into a sport with contact in the ring. Some advocates prefer to limit themselves to just stand up fighting, or throwing style fights such as judo, or perhaps grappling. There are so many things to learn that it becomes questionable whether one could possible master more than just a part of several styles.
For those who wish to add a character or philosophical side to the various martial arts, many styles codify their systems and require the students to abhere to rigid codes of conduct. This conduct generally means using the art form for the good of the community and to protect others. In Japan a person would then study karate-do (pronounced doh) as a path or way of karate.
Many classical Japanese styles have this suffix 'do' to indicate they are more than just a technical fighting system. For example, judo, aikido and kendo all have inherent conduct codes built into the learning. These more classical systems are in contrast to modern approaches that emphasize the martial arts as sporting activities with competition for medals as the key goal.