Why ";" must be breaker of the code

Question

example : "echo 'test';"

Answer 1

Few of the symbols are choosen to be reserved for a specific purpose, which are mostly common to all programming as well as scripting languages.
Here ; (semicolon or terminator) is ised for termination of a statement.

And your example is errornous.
Correct one is- <php echo "test"; ?>

Answer 2

it is the default rule of PHP syntax.
you will find ";" with the same function in other language, like c++.