I have attached the relevant picture below. Unfortunately, I do not even know the name of this dot symbol that is being used in this equation; otherwise I could have google'd what it represents. By dot, I am referring to the $(L_{uu}^{-1})_{\cdot k}$ and $(L_{uu}^{-1})_{k\cdot}$
Note that $u$ is a set of indices of $L$. So $L_{uu}$ is a submatrix obtained from the elements of $L$ corresponding to the row and column indices in the set $u$. Also note that $k$ is some index $k \in u$.
I will take a wild guess and say they refer to the k-th column and row of $L_{uu}^{-1}$, which would mean the numerator in the second term on the RHS is an outer product.
Its a wildcard character. $M_{\cdot j}$ means the the $j$-th column of $M$, while $M_{j\cdot}$ means the the $j$-th row. In linear algebra literature, it is much more common to use an asterisk (i.e. to write $M_{\ast j}$ and $M_{j\ast}$) than to use a dot for rows and columns.