Sequences are dynamically sized arrays (<https://narimiran.github.io/nim-basics/#_sequences>, <https://nim-lang.org/docs/system.html#system-module-seqs>).
I recommend you checking out a tutorial (like the one linked) to learn about fundamental Nim data types like sequences. Unicode operators can be found in the manual here: <https://nim-lang.org/docs/manual.html#lexical-analysis-unicode-operators>
