Matrix Chain Multiplication

what is the exact meaning of dimentionality used in this concept, and how it is n+1 for n matrices

could u tell me the point where he mentioned the word

becase when if u see for 2 matrix
we incurred the cost r1 * c1 * c2
that is for 2 matrix 3 elements add up to cost
same way n would have n+1 elements adding to cost