origin: (2003) Maria Thomas & Rick Roberts: "Zen" + "Tangle"
A form of art developed & marketed by Rick Roberts & Maria Thomas, respectively a Zen monk and a calligrapher (the tangle). The coining of the word is said to come about from a day when Rick could not get Maria's attention as she was so absorbed in her work -- she wasn't ignoring him, but literally had not heard him -- astounded at a level of concentration that normally took ascetics decades of training to master, they began to work together to promote a relatively simple form of art that they hoped would bring inner peace to the masses.
With the catchphrase, "Anything is possible...one stroke at a time", they developed a flexible method of techniques to welcome all ages, races, and skill levels. Typically creating (though not exclusively) black & white images, sectioned by lines and filled with patterns; images within images; worlds within worlds. This differs from doodling, as it is a focused method of style versus a subconscious one and there is a consistency to the appearance despite the many possible variations. World-renowned Japanese artist, Yayoi Kusama, utilizes a similar technique in her surreal exhibitions.
One can easily access zentangle techniques through Youtube as well as Pinterest.