A tendu is a basic ballet term refering to the action of extending a pointed foot out from a postion with a straight let and your toe is still maintaing contact with the floor. This can be done in preparation for another step, often a turn, or center floor in technique courses and performed from any position. En dedans refers to the directional pattern in which the tendu would be completed. in this case "tendu en dedans " would mean that this is an exercise being execuated from any given position forwards, sideways, backwards, and sideways again starting in a clockwards motion. If you use the numbers on a clock as reference it would be that your foot would first point in front at 12, to the side at 3, to the back at 6, and then again to the side at 3.
A piroutte is a turn where one leg is in releve ( on toes or en pointe ) and the other is in raised in retire ( meaning the toe is pointed and connecting to the knee with the knee bent to the side in a number 4 shaped motion) En dehors refers to the direction of travel simply meaning counter clockwise, turning inside towards your body instead of outwardly and travelling.