noun
Used as a time unit, identical to the English 'second'. Common in technical, sports, and everyday timing contexts.
100メートルを11セコンドで走った。
He ran 100 meters in 11 seconds.
あと30セコンドでタイムアップです。
Time's up in 30 seconds.
noun
Primarily used in boxing and combat sports for the person who assists a fighter between rounds. Can also refer to a helper or trainer in other sports contexts.
ボクサーはラウンドの合間にセコンドからアドバイスを受けた。
The boxer received advice from his second between rounds.
彼は試合でセコンドを務めた。
He acted as a second at the match.