This is a method or sub-command of the Emoji command. It is not its own command.
This command can be used to search for a custom emoji within a server using keywords. This is useful if there are a lot of emojis in a single server (With boost levels) or if many emojis looks very similar in the emoji-picker.
This command will not search through default Discord emojis and will also not search through other custom emojis from other servers, even if you are the owner of them too.
The search is a loose match, meaning that the letters in the keyword must in the correct order for the emoji to be a match, but the keyword you enter can be located anywhere in the emoji name itself. The search will only work with Alphanumeric characters (Letters and numbers).