Kamae in the martial arts refers to ways of moving and holding the body, we have postures where the arms are held up in a defensive posture, while the legs shift back in order to keep one away from danger- ichimonji no kamae as an example.
When we interact with our training partner during practice there are many vulnerable points on the body and it is kamae that is used to protect them.
(These weak points are called kyusho.)
By positioning the arms and feet in select ways you prevent your training partner from being able to attack these weak points. Assuming these postures is the first step in self-defense as they make it harder to be effective attacked.
At these same time, using the correct kamae, if one is attacked it forces the attacker to navigate through them- exposing their weak points (kyusho) which helps to make your self-defense movements easier.
Kamae are also used to control distance and timing of both you and your training partner which adds another layer of self-defense.
For a greater understanding of the importance of distance and timing please check out our training PDF guide: Movement in the Martial Arts which can be downloaded off our site here.
Kamae of budo taijutsu: ichimonji, jumonji, hicho, doko, hira ichimonji, hoko, and fudoza.