Some articles on entourages, entourage:

Uniform Space
... X (Φ is called the uniform structure or uniformity of X and its elements entourages (French neighborhoods or surroundings)) that satisfies the ... On a graph, a typical entourage is drawn as a blob surrounding the "y=x" diagonal the U’s are then the vertical cross-sections ... An entourage U is symmetric if (x,y) ∈ U precisely when (y,x) ∈ U ...