I assume you mean the cartilage
between the femoral condyle and the tibial plateau.
This would be the meniscus, a c-shaped/half-moon shaped cartilage. If on the inside, it's called the medial meniscus, and if on the outside, the lateral meniscus. The other type of cartilage in the knee is called articular cartilage. It covers the bones that make up the knee joint, like frosting on a cake.