A charge, cost, or price (often used as a suffix indicating a fee or price range).
ガス代が先月より高くなった。
The gas bill got higher than last month.
宿代は一泊一万円です。
The lodging charge is 10,000 yen per night.
タクシー代は会社が払います。
The company will pay the taxi fare.
この本は千円代だ。
This book is in the thousand-yen range.
Generation, age group, or cohort (used as in '〜dai' for decades of age, school year/cohort, or a generation/reign).
彼は30代だ。
He is in his thirties.
私たちの代はスマートフォンが身近にあった世代だ。
Our generation grew up with smartphones being commonplace.
今年は私の代のクラスメイトが同窓会を企画している。
This year my cohort/class year classmates are organizing a reunion.
An era or geological period (used in geology to denote periods such as Paleozoic, Mesozoic, etc.).
中生代は恐竜が栄えた時代だ。
The Mesozoic era was when dinosaurs flourished.
地質学では古生代・中生代・新生代と大きく分ける。
In geology, periods are broadly divided into the Paleozoic, Mesozoic, and Cenozoic eras.
Used after a name or title to indicate representation or acting on behalf of someone (commonly seen in documents or attendance lists).
議事録には『山田（代）』と記載されていた。
The minutes recorded 'Yamada (代)' (indicating someone is attending on Yamada's behalf).
会には部長の代で係長が出席した。
The section chief attended the meeting on behalf of the manager.
A notation used after a phone number to indicate the company's main/representative number (seen as '（代）' on business cards).
名刺に「03-1234-5678（代）」と記載されている。
The business card lists '03-1234-5678 (main number)'.
A counter for decades of age or for indicating a particular era/decade (as in '〜s', e.g., the 1980s).
彼は40代後半に入った。
He has entered his late forties.
昭和40年代の音楽がまた人気になっている。
Music from the 1960s (Showa 40s) is becoming popular again.
A counter for generations (used to count successive generations or holders, e.g., three generations).
この店は三代続いている。
This shop has been in the family for three generations.
その家は四代にわたって同じ屋号を使っている。
That family has used the same trade name for four generations.
As an abbreviation, it can indicate a proxy application company or similar (used in administrative notes/documents).
今回の申請は代（代理申請会社）に頼んだ。
We asked a proxy application company (代) to handle this application.
An abbreviation in dictionaries where '代' stands for 'pronoun' (used in headword classification).
辞書の見出しで『代』とあれば、代名詞を示している。
If a dictionary entry shows '代', it indicates a pronoun.