A century — a period of one hundred years; a chronological unit used to divide history (e.g., the 20th century).
20世紀は科学と技術の進歩がめざましかった。
The 20th century saw remarkable advances in science and technology.
21世紀に入ってから情報技術が急速に発展した。
Since entering the 21st century, information technology has rapidly developed.
その建物は19世紀に建てられた。
That building was built in the 19th century.
An era — used to refer to a particular period characterized by distinct features; century used figuratively as an age or epoch.
産業革命は新しい世紀の到来を象徴する出来事だった。
The Industrial Revolution was an event symbolizing the arrival of a new era.
この発明は音楽の世紀を変えたと評された。
This invention was said to have changed the era of music.
Used in expressions like 'of the century' (e.g., 'fight of the century') to emphasize something exceptionally important or noteworthy.
彼らの試合は『世紀の対決』と呼ばれた。
Their match was called the 'fight of the century.'
世紀の発見として科学界に大きな衝撃を与えた。
It gave a major shock to the scientific community as a discovery of the century.