I was confused, so a while back, I wrote to Zentangle.com and asked what a zentangle was, and how it differed from a zendoodle. Here is the reply:
Thanks for writing.
Our core concept is to use a "string" which defines an area (this is usually done in pencil) and then that area is filled in with a repetitive pattern chosen from an existing list of patterns, or "tangles." There is much more, such as using good tools, not being concerned with up/down orientation, shading, etc. - much of which is on our website. Our string and tangle approach is an essence of Zentangle.
Perhaps I'm mistaken, but I believe that "zendoodle" is a term that folks came up with because of the unnecessary fear of copyright infringement.
We are quite happy and thrilled that people are inspired by Zentangle to create art that they might not have otherwise done. That they call it a zentangle, or Zentangle-inspired art, makes perfect sense.
There is other information available on this subject--a great deal of it coming from Sandra Bartholomew, who is a certified zentangle teacher. Her blog is invaluable to anyone interested in zentangling and learning new patterns. She has written an article that was published in the Nov/Dec issue of Cloth, Paper, Scissors, and several of her posts explain more about what the zentangle is or isn't.
Here are a list of links to information about zentangles that I found enlightening:
How to zentangle-probably the most specific information of the traditional zentangle technique and tools:
Article written by Rick and Maria:
Sandra Bartholomew's essay on misunderstanding the zentangle:
About Article in Nov/Dec Issue of Cloth Paper Scissors magazine.
Article in New Hampshire magazine (not quite correct in what it says)
I think all the experts agree on one thing when it comes to zentangling. You are meant to enjoy yourself. If what you do doesn't quite fit the definition--so what?