"red sheet", specifically a red translucent plastic sheet used in studying to render red-colored text illegible

(Internet slang) secret personal account (on social media, especially Twitter and Instagram (finsta), as opposed to one's openly used account)

Red alpenglow of Mount Fuji in the morning, especially in early autumn.

(Internet slang) protected account (on social media, especially Twitter and Instagram)

red dragonfly (generic term)

(idiomatic) make no progress, remain unsettled

red hair

(mahjong) red tile; unique to Japanese mahjong and used to score bonus points

(Internet slang) having multiple accounts

(Internet slang) alt (account)