PHP tags are used to embed PHP code in HTML. The types are:

• Standard tags: <?php ... ?> (recommended and always available)
• Short echo tags: <?= ... ?> (for outputting, always enabled in PHP 5.4+)
• Short tags: <? ... ?> (not recommended, requires short_open_tag enabled)
• ASP tags: <% ... %> (removed in PHP 7.0)

Standard tags are recommended for maximum compatibility and clarity.