noun
armband
A band worn around the upper arm, often for identification, fashion, or sports. The English loanword is used in Japanese with the same meaning.
ランニング中にスマホを入れるアームバンドを使っている。
I use an armband to hold my phone while running.
イベントスタッフは全員、黄色いアームバンドを着用して
All the event staff were wearing yellow armbands.