"fluid boundaries" is correct and usable in written English.
You can use it to refer to boundaries that are not fixed or permanent and can change or be crossed. For example, you could say: "The concept of fluid boundaries makes it difficult to define exactly what qualifies as a particular type of person or thing."
For Mr. Kon the fluid boundaries between dimensions simply reflect the world as we experience it.
Fluid boundaries between the seen and the unseen, the known and the unknown, continue to flourish.
"Having fluid boundaries and keeping your geography open" comes first, she said, elaborating on an entry in the chapter of "The Boomers' Guide" called "The Search Is On".
Ours is an age of fluid boundaries and of a drastically lowered general threshold of embarrassment, so one might suppose that the genre would be obsolete.
American conceptual artist and sculptor who created art from an approach that valued fluid boundaries between artistic disciplines and playful engagement with the viewer.
For Americans at the time, the cases — much like the contemporary controversy over "Innocence of Muslims" — were a reminder of the fluid boundaries of our liberties, that an open society must not only protect rights but also balance them.
This startling case highlights the fluid boundary between biography, artistic licence and China's totalitarian legal system.
"For young people, there is rather a kind of fluid boundary between the real and virtual world, and they can easily pass through it," she said.
In the enterprise, we're transitioning to a way of working that is far more fluid, boundary-less and social.
Endocardial displacement was applied to fluid boundary using fluid structure interaction (FSI) approach.
Quadratic conforming boundary elements are used to discretize the fluid boundary.
