A permutation is an arrangement of objects in a specific order. In combinatorics, a permutation is a rearrangement of items from a set such that each item appears exactly once. A permutation can be represented mathematically using the notation P(n,k), where n is the total number of items in the set and k is the number of items being arranged. The result of P(n,k) gives the number of possible permutations of k items that can be selected from a set of n items. It's important to note that the number of permutations is different from the number of combinations because the order of the items is considered in permutations. This concept has important applications in many fields, including computer science, cryptography, and statistical modeling.
The difference between permutation and combination lies in the fact that permutation considers the order of the elements, while combination does not.

Permutation is an arrangement of objects in a specific order, whereas combination is a selection of items from a larger set where the order of the items is not important.

Mathematically, a permutation is represented as P(n,k), where n is the total number of items in the set and k is the number of items being arranged. The result of P(n,k) gives the number of possible permutations of k items that can be selected from a set of n items.

On the other hand, a combination is represented as C(n,k), where n is the total number of items in the set and k is the number of items being selected. The result of C(n,k) gives the number of possible combinations of k items that can be selected from a set of n items.

In summary, permutations are arrangements that take into account the order of the elements, while combinations are selections that do not consider the order.