Order Set Theory

I understand order and repitition of elements does not matter when talking about sets. However, multisets have it so repitition of elements does matter. Is there another specific type of set where order matters?

• I've adjusted the tags - "elementary-set-theory" is more appropriate for this type of question, and descriptive set theory refers to a specific subfield of mathematical logic. – Noah Schweber Jan 21 '17 at 16:20

A Tuple is a finite ordered list of elements. Multisets do not care about order, just about how many of each element there are, so as multisets $\{1,1,2\}=\{1,2,1\}.$ Sequences can be finite or infinite but care about order.