Basic understanding :
In client server architecture
Server :> Which serves the requests.
Client :> Which consumes service.
Web server & Application server are both software applications which act as servers to their clients.
They got their names based on their place of utilization.
Web server :> serve web content
:> Like Html components
:> Like Javascript components
:> Other web components like images,resource files
:> Supports mainly web protocols like http,https.
:> Supports web Request & Response formats.
Usage --
we require low processing rates, regular processing practices involves.Eg: All flat servers generally available ready-made which serves only web based content.
Application server :> Serve application content/component data(Business data).
:> These are special kind which are custom written
designed/engineered for specific
purpose.some times fully unique in
their way and stands out of the crowd.
:> As these serves different types of data/response contents
:> So we can utilize these services for mobile client,web
clients,intranet clients.
:> Usually application servers are services offered on different
protocols.
:> Supports different Request& Response formats.
Usage --
we require multi point processing, specialized processing techniques involves like for AI.Eg: Google maps servers, Google search servers,Google docs servers,Microsoft 365 servers,Microsoft computer vision servers for AI.
We can assume them as tiers/Hierarchies in 4-tier/n-tier architecture.
So they can provide
load balancing,
multiple security levels,
multiple active points,
even they can provide different request processing environments.
Please follow this link for standard architecture analogies:
https://docs.microsoft.com/en-us/previous-versions/msp-n-p/ee658120(v%3dpandp.10)