Roll- This movement is one of the most important in all of parkour. It is a true multitasker and is used to transfer shock, regain composure after a flip or other technique where you may end up off balance, and it can be used to save oneself from injury. What you basically do in this movement is place hand on ground, absorb shick slightly with arm then roll across the arm to the shoulder while tucking and as you roll your body should roll from shoulder to the opposite hip then push of with the leg and keep running.
Notes- The technique is relatively simple to learn but difficult to master.There are many different techniques to the roll as well as variations on the way you roll or the direction you roll(backward roll, Forward, left, right).
you need to find the technique which works best for you. If you do martial arts ( as I do) just use the same technique as you do in your dojo and you should be fine, a gymnastics roll however is not acceptable as it is a dangerous technique when used on the concrete and can lead to injury. when Rolling after a drop you want to sort of melt into the ground , absorb the shock with legs slightly and project yourself forward and roll. when absorbing shock for the roll you don't want to bend the legs farther than a 90 degree angle otherwise it could lead to undue strain on the knees and/or slamming of the knees into the ground.
Dive roll-For this movement you run, jump and project yourself forwards in a similar fashion to a kong/saut de chat and you want to bend yourself slightly, place arms in front of you at a lightly offset angle and as soon as they touch the ground you want to absorb the shock slightl with the arms, tuck, and follow though with way you traditionally roll
Notes-This movement is technically more difficult than the traditional roll but is used instead to dive over an object, roll and continue on. For this technique you should not practice diving over something first ( instead practice in grass or gym). Also do not try this until you are extremely comfortable with the regular roll.
French name-----Roulade
Hope this is accurate and makes sense.... keep running