“sage” is a bulletin board feature that lets users post in a thread without actually bumping it. It was first introduced to 2channel on December 2, 1999 as “aburanuki” (油抜き, lit. “putting out oil”) but nobody liked it, so it was changed to “sage” for “sageru” (下げる, lit. “to lower”).

This feature is used by inputting “sage” in the email field when posting. Any variants (e.g. “SAGE”, “ｓａｇｅ”, “さげ”, “サゲ”, etc.) simply won't work. On 2channel, use of “sage” is encouraged to help threads maintain a relaxed atmosphere, possibly since trolls often target front page threads which may explain why these boards still don't have pagination. It was also the only way to get sent back to the thread back then.

Unfortunately, this concept is lost on imageboards like Futaba Channel and most non-Japanese boards due to board pagination and how there's no incentive for using it, so it sticks out since people don't really use it. On non-Japanese boards, some users treat “sage” as a trump card to invoke hostility and derail threads into a cyclical argument on bumping, thus why 4chan made it invisible.¹⁾

• The antonym of “sageru” (下げる) is “ageru” (上げる), therefore the antonym of “sage” is “age”.
• In the early days of 4chan and on Kareha boards like 4-ch, using “sage” on a board with IDs enabled would result in “ID: Heaven” being the unique identifier.
• For some reason, it was only ever used properly on 4chan's /jp/ board.

• Sage on Niconico Encyclopedia
• Sage Progression on 2channel's Wiki