Everything inside a pair of opening and closing tag is interpreted by php parser. Php introduced three types of opening and closing tag.
1.Standard tags

2.Short echo tag

here, 

Standard tag and short echo tag are alwayes available.
But short tag can be disabled either via the short_open_tag php.ini configuration file directive, or are disabled by default if PHP is built with the --disable-short-tags configuration.

If a file contains only PHP code, it is preferable to omit the PHP closing tag at the end of the file.
This prevents accidental whitespace or new lines being added after the PHP closing tag