What does PHP API mean in phpinfo?

Question

PHP

When I updated PHP not from the native Ubuntu repository, but from the connected one, I met with the fact that some of the PHP extensions refused to work due to incompatibility. Explain clearly the meaning of these directives, how they are formed and what else they affect:

PHP API
20131106

PHP Extension
20131226

Zend Extension
220131226

Zend Extension Build
API220131226,NTS

PHP Extension Build
API20131226,NTS