Say

Minecraft command for broadcasting messages.

This command allows for natural display of text through interaction of the player.
start the command with /say.
Then your message!

The full command will be like /say <message>.
This is where <message> is like a greedy phrase where it takes all words and symbols after the command is invoked.
This also means that you can't format the <message>.

Selectors

The /say command does allow to parse <selector> arguments like @s or @e and return the output of the entity type or player name.

Server side

This command is easy for server or datapacks themself to run quick test commands! Output will usually look something like this when ran in the server console.

[Render thread/INFO]: [System] [CHAT] [Server] Hello World

Command block output

When running /say through a command block it outputs as an entity with name @ because of its empty selector.

[Render thread/INFO]: [System] [CHAT] [@] Hello World

Use cases

Useful for a quick debug when coding a datapack or adventure map.
Great for when you want to broadcast messages to console.
Useful for sending messages through server console.

Reference

Information:
https://learn.microsoft.com/en-us/minecraft/creator/commands/commands/say?view=minecraft-bedrock-stable
https://minecraft.wiki/w/Commands/say#:~:text=JE:%20:%20message,used%20to%20mention%20all%20players
https://www.minecraftforum.net/forums/minecraft-java-edition/redstone-discussion-and/commands-command-blocks-and/2525680-the-say-command#:~:text=vague%20and%20unhelpful.-,"/say%20@a"%20I%20understand%20as%20%27announce%20to,https://discord.gg/QAFXFtZ