先入 さきい先出 さきだしリストでしょう
sakiiresakidashi risutodeshō

Noun
Desu Copula

Expresses probability in a polite manner ("probably…") of 先入れ先出しリスト

1. First-come, first-served list; Probably a first-come, first-served list.

Polite
Presumptive
Conjecture
Computing