What are placeholders (or markers) in an HTML document that the web server will dynamically replace with data just before sending the requested documents to a browser?

What are placeholders (or markers) in an HTML document that the web server will
dynamically replace with data just before sending the requested documents to a browser?

A.
Server Side Includes

B.
Sort Server Includes

C.
Server Sort Includes

D.
Slide Server Includes