Kenjutsu is the art of fighting with swords.
Many shinobi can learn it and although not exclusive to Kiri and Kumo, those two villages place greater emphasis on kenjutsu than do the other villlage. Specifically, Kumo has their own kenjutsu technique and Kiri has the seven ninja swordsmen of the mist.
Aditionally, kenjutsu is the primary fighting style of the samurai descended from the Land of Iron. The samurai are able to channel their chakra into their swords to enhace their power (it was notice that when Sauske channeled his chiodori nagashi into his blade that the technique bared resemblenced to the techniques of the samurai).