A differential operator of second order $f=f(\cdot,u,Du,D^2u):\mathbb{R}^n\times\mathbb{R}\times\mathbb{R}^n\times\mathbb{R}^{n\times n}\to \mathbb{R}$ is said to be degenerate elliptic, if
$\forall A\leq B \,\,\text{in}\,\,\mathbb{R}^{n\times n}\,\,\,\,$ $\Longrightarrow$ $\,\,\,\,f(a,b,c,B) \leq f(a,b,c,A)\,\,\,\,$ for all $(a,b,c)\in\mathbb{R}^n\times\mathbb{R}\times\mathbb{R}^n$
holds. With $A\leq B\,\,\text{in}\,\,\mathbb{R}^{n\times n}$ we mean that $B-A$ is positive semidefinite.
How does this compare to usual (uniformly) elliptic differential operators? Is it a weaker concept? I can't really see how they relate...
Thanks in advance!