The place on the chromosome around the centromere where the spindle fibers attach to the chromosome.
The kinetochore is actually composed of several proteins that attach to the proteins that make up the centromere. The microtubules (spindle fibers) attach to the centromere as they grow. Usually, there is a "sister kinetochore" to go with each "sister chromatid". Thus, the kinetochores, along with the chromatids, segregate during mitosis and during meiosis II.