Glissade is a classical ballet term meaning “glide.” It is a traveling, usually small, jump that is usually used to link other steps together. It can be considered an in-between step.
A dancer performs a glissade by plieing in fifth position, sliding (or gliding) one foot out into a degage side. The working leg reaches about 20 degree off the floor, the dancer pushes off the supporting foot and extends it to the side. For a moment, the dancer is in the air with both legs and feet fully stretched and pointed as if in a sauté in second position. The working leg then lands on the floor as the supporting leg (in the air already) quickly closes into fifth position.
Glissade is usually done with the back foot starting outwards first and not changing position as you land into fifth. Meaning, if the right leg started in the back and slid out to start, it will also end in the back. However, some schools teach that glissades change feet positions as they’ve landed. Both are considered correct.
Glissades can also be done to the front or back or on the diagonal. They are most commonly done on the diagonal in grand allegro to provide more power and rhythm for jumps. A glissade is very often performed just before a sauté chat, a cabriole and many other big jumps. In petit allegro, glissades are often in-between steps for assemblés and jetes.