x y is by default interpreted as CenterDot[x, y].
Used to indicate various forms of multiplication, particularly dot products of vectors.
Sometimes used to indicate concatenation or composition.
Used in the British mathematical tradition as a decimal point.
See The Mathematica Book: Section 3.10.1 and Section 3.10.4.
See also: \[CenterEllipsis] , \[RawDot] , \[CircleDot] .