iMessage is Apple's proprietary chat protocol. It's still named that -- for instance in iMessage apps and iMessage stickers. "Messages" is the current name of t

iMessage is Apple's proprietary chat protocol. It's still named that -- for instance in iMessage apps and iMessage stickers. "Messages" is the current name of the user facing app that speaks both iMessage and SMS, which was formerly named "Text" when it just used SMS. I think you're thinking of the defunct iChat message client on macOS.