What is the meaning of "\;" in "find" command? [duplicate]

The find command has to have a way of telling where the command that should be executed through -exec ends. Without the ; at the end of the command, find would not know where the command ended and where (possibly) other find flags continued.

A nonsensical example that executes basename on all files and ls on all directories:

find . '(' -type f -exec basename {} ';' ')' -o '(' -type d -exec ls {} ';' ')' 

Without the ; above, find would not know whether to execute basename /some/path or basename /some/path ')' -o '(' ... etc.

Quoting or escaping the ; is only done so that the shell will not treat it as a command delimiter.

A less nonsensical example that first copies .txt files to a particular directory and then renames the original files by appending .done to their name (if the copying went ok):

find . -type f -name '*.txt' -exec cp {} /some/path/dest ';' \ -exec mv {} {}.done ';' 

(Note, as Eliah Kagan points out in comments, that the construct {}.done is strictly speaking not portable, but implementation defined. An implementation may choose not to expand the {} characters to the current pathname, or it may do. In my experience, all find implementations do expand {} to the current pathname even when concatenated with another string like this.)

Without the ; in the previous example, find would not know whether we would want to execute the cp command on the found file together with /some/path/dest, a file called -exec, mv etc.