Manual for Ubuntu's break command

"For Bash:

$ help break
break: break [n]
Exit for, while, or until loops.

Exit a FOR, WHILE or UNTIL loop. If N is specified, break N enclosing
loops.

Exit Status:
The exit status is 0 unless N is not greater than or equal to 1.

The error message you are seeing is issued by Bash. What is the context in which you are trying to understand ""break""?

In C, break is a keyword. See this wikibook for more information. In part, it says:

A break statement will immediately exit the enclosing loop."

A googling came up with this link, suggesting that the break command you've come across is indeed not from bash; it's from zsh. Hence you should be able to get the correct manual by issuing man zshbuiltins.