Servlet versus JSP

Both a servlet and JSP are "called" with a reference to to them as a web page, but they are executed differently and used for different types of problems.
A servlet is a complete Java program that generates browser-readable output (typically HTML). (So, HTML embedded as output in Java code.)
JSP is snippets of java code embedded in an HTML page. (So, Java code embedded in HTML.)
Servlets are compiled once, then the .class file is executed by the container (i.e. TomCat).
JSP is compiled each time it is executed, so a syntax error results in a "run-time" error.
Servlets are server processes, so once they start, they continue running.
Servlets are multi-threaded - to handle each Client request, a new thread is executed on the Servlet object.
JSP is re-executed each time it is "called".