What is this? I can't find help by using
It's a matrix multiplication operator!
From the documentation:
Multiplies two matrices, if they are conformable. If one argument is a vector, it will be promoted to either a row or column matrix to make the two arguments conformable. If both are vectors of the same length, it will return the inner product (as a matrix).
x %*% y
ynumeric or complex matrices or vectors