Which term best describes the idea that no arrangement order matters in a selection process?

The term that best describes the idea that the order of arrangement does not matter in a selection process is "combination." In combinations, the focus is on selecting items where the arrangement or order in which they are selected is irrelevant. This means that if you have a group of items and you select a subset from it, the different arrangements of that subset do not count as unique selections.

For example, if you have the letters A, B, and C, and you choose 2 letters, the selection "A and B" is considered the same as "B and A." Hence, combinations are used in scenarios where the arrangement does not influence the outcome, such as in lottery drawings, group selections, or any situation where the focus is only on the items selected, not the order in which they are arranged.

Understanding this concept is fundamental when distinguishing between combinations and permutations. In permutations, the order of selection is essential, which is why that term does not fit the definition given in the question.