Multiple threads or app instances?

ASP.NET QuickStart Tutorial says that:
....
ASP.NET maintains a pool of HttpApplication instances over the course of a
Web application's lifetime. ASP.NET automatically assigns one of these
instances to process each incoming HTTP request that is received by the
application. The particular HttpApplication instance assigned is responsible
for managing the entire lifetime of the request and is reused only after the
request has been completed. This means that user code within the
HttpApplication does not need to be reentrant.
....
A Note on Multiple Threads

If you use objects with application scope, you should be aware that ASP.NET
processes requests concurrently and that the Application object can be
accessed by multiple threads....
To make this code thread safe, serialize the access to the Application
object using the Lock and UnLock methods.
....

What do all above mean? ASP.NET/IIS launches multiple web applications for
every
request/session or one application (which starts when first request comes)
with multiple threads where each thread is responsible for each
request/session?


.

Relevant Pages

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