This is a very difficult question to answer in a few sentences!
Aikido is a Japanese martial art developed by Morihei Ueshiba (O Sensei) in the
1930s to the 1960s. Morihei Ueshiba dedicated a large part of his life to the study
of many martial arts disciplines including schools of sword, spear, knife, shuriken
and empty-handed technique all of which contributed to the aikido he demonstrated.
The aikido that O Sensei taught varied throughout his life and students who saw him
at particular times often show very different interpretations of his teachings.
The name 'aikido' is composed of three Japanese characters: 'ai' meaning 'harmony', 'ki' meaning '(vital) energy' and 'do' meaing 'way'. So 'aikido' means The way of Aiki, or harmonising with energy, the energy of our attacker and the energy of ourselves.
There are no competitions in traditional aikido. Practioners alternate the roles of uke (attacker) and nage (defender) to practice the art of recovery and technique respectively. For more information on what aikido is or isn't, you can find a wealth of information on the web with very little googling (or see some of our links) or better still step on the mat when you're ready.
There are three basic weapons we use in aikido training: tanto (the knife), jo (wooden staff), bokken (wooden sword). We practice weapons for a variety of reasons, firstly weapons are symbolic of their sharper and less beginner-friendly counterparts (!) and thereby give us an insight into the origins of the technique as well as its practical application.
Secondly, weapons extend the reach of ourselves and our training partners, helping us to develop our timing and spatial awareness. Also weapons can provide a silent commentary on the efficiency of our own movement, highlighting issues we could more easily overlook without them.
For a much more in-depth look at different aspects of aikido, please read through the Aikido Primer, reproduced here by kind permission of the author, Eric Sotnak.
"Do not look upon this world with fear and loathing. Bravely face whatever the gods offer"
Morihei Ueshiba