What exactly is an application pool? What is its purpose?
IIS-Internet information Service is a web server used to host one or more web application . Lets take any example here say Microsoft is maintaining web server and we are running our website abc.com (news content based)on this IIS. Since, Microsoft is a big shot company it might take or also ready to host another website say xyz.com(ecommerce based).
Now web server is hosting i.e providing memory to run both websites on its single web server.Thus , here application pools come into picture . abc.com has its own rules, business logic , data etc and same applies to xyz.com.
IIS provides two application pools (path) to run two websites in their own world (data) smoothly in a single webserver without affecting each ones matter (security, scalability).This is application pool in IIS.
So you can have any number of application pool depending upon on servers capacity