Second in order; the ordinal meaning 'second' (e.g., the Second World War, Chapter Two).
第二次世界大戦は20世紀前半の重要な出来事だ。
The Second World War was a major event in the first half of the 20th century.
この本は第二章が一番面白い。
The second chapter of this book is the most interesting.
彼は部署で第二のポジションに昇進した。
He was promoted to the second position in the department.