First, a description and definition of jiu-jitsu (Japanese pronunciation: djoe djitsoe) is in order. Generally, jiu-jitsu is translated as the "soft art" (ju or jiu = soft, accommodating; jitsu = art, skill). Although jiu-jitsu may not come across as "soft" at first glance when you see a training or demonstration, there is a great deal of truth in this translation. A jiu-jitsuka (practitioner of jiu-jitsu), when attacked, will prefer to go along with the attacker's movement. A karateka, for example, will block an attack and then place a counter punch. This is a fairly hard form of defense. Jiu-jitsu focuses on using the energy of the attack. If you are pushed, for example, you can use the forward energy exerted on you to initiate a hip throw to floor the attacker (uke). Instead of countering, you join in the movement after which a throw, clamp or atemi (kick or punch) decides the situation in your favor.
A comprehensive definition of jiu-jitsu is difficult to formulate. Although jiu-jitsu is focused on self-defense, it also includes aspects that can be used for offensive purposes. For example, for the 2nd dan exam you have to show acquisitions where the attacker wins. Sometimes the attack is also the best defense (for example, with multiple opponents). Although we usually work unarmed we must also be able to defend against attackers with weapons (e.g. stick or knife). It is often also useful to be able to handle these weapons ourselves. The stick you took from a disengaged attacker can be used against other attackers. Serge Mol gives a good description of traditional jiu-jitsu in his book 'Classical fighting arts of Japan':
"A method of close combat, either unarmed or employing minor weapons, that can be used in defensive or offensive ways, to subdue one or more unarmed or armed opponents.
But modern jiu-jitsu largely includes athletic competition. Purists may raise the objection that competitive jiu-jitsu provides a content limitation because the most dangerous (and often most effective) techniques may not be used. On the other hand, however, sporting success often generates much positive publicity that ensures that jiu-jitsu becomes more widely known.
Jiu-jitsu is one of the oldest martial arts still practiced today. Jiu-jitsu was practiced by the samurai class of the Japanese Middle Ages. The samurai were Japanese knights who served a Japanese nobleman (shogun) with the main purpose of protecting the lord and fighting in war on the field of battle. Hence, jiu-jitsu is also called a martial art or martial art. A samurai's main weapon was his sword (katana) but if they were disarmed in battle they also had to be able to continue fighting. Jiu-jitsu was developed for this purpose. In traditional forms of jiu-jitsu, defenses against the sword often occur.