Is DevSecOps indeed a new practice worth a professional term? Or rather marketing slang? 
Currently, I am not always sure how to build a consense which words deliver informational value and which are thought to attract customers.
So, DevOps would include security testing if required without calling it DevSecOps? Otherwise we will have DevPerfOps,  DevDevOpsOps etc
In my experience, the purpose of the "DevSecOps" (or whichever order you prefer) has mostly to do with including Security as a first-order concern of software delivery.  Security is commonly treated as a "bolt-on" (often meaning optional,) non-functional requirement.  DevSecOps attempts to describe a process where security concerns are folded into the delivery process at every step of the value stream.