Kendo uses mainly two swords; the most common is the shinai (竹刀; lit. bamboo sabre) that is made of four bamboo slats tied together by pieces of leather, the other is the bokuto (木刀; lit. wooden sabre) or bokken (木剣; lit. wooden sword) and is made of solid wood (usually oak).
The shinai is used for actual practise (duels and stuff), it's shape is designed solely for the purpose of safety and thus it doesn't really look like a real sword, but it's the best way to do some impact-practise in kendo without severely injuring someone.
The bokuto is basically a katana made of solid wood, it was created to be a cheaper substitute to the steel sword (back in samurai days you wouldn't want to waste your katana in a training session) and it tries to simulate a steel sword in almost every aspect. In modern kendo, the bokuto is used mainly in kata and other non-impact exercises. The use of the bokuto mantains the kendoka closer to the feeling of the real katana.
Experienced kendokas can also use real katana instead of bokuto, and it's called shinken (真剣) when it's sharp.
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