It is a technique used to let the subconscious mind flow. It is executed quickly with simple lines or shapes, usually without any reference material.
Types
Zentangle
Zentangle is an easy to learn, relaxing and fun way to create beautiful images by drawing structured patterns. The process is a form of “artistic meditation” as one becomes completely engrossed in making each pattern, deliberately focusing on each stroke. The Zentangle art form and method was created by Rick Roberts and Maria Thomas. Zentangle® is a registered trademark of Zentangle, Inc. You can learn much more at zentangle.com
Zendoodling
Zendoodling is doodling as a form of meditation.