What is the "APM, Web Application" module used for?

Is this on the license screen?

A web application means you can have a application that is configured in LTM and you can put an authentication front end on it using APM. This is called APM+LTM mode. It means you can add authentication using AD, LDAP, Certificate, Tacacs, Radius, Kerberos, NTLM, etc including 2FA to the authentication for that application. Then you can pass the relevant bits to the application so it logs in automatically using the credentials supplied to APM by the user.

I have the same question... I normally see "APM, Base CCU XXXX" or "APM, Max CCU XXXX" when APM is licensed, but it isn't clear if this "APM, Web Application" refers to the so called APM light mode....

BIG-IP Access Policy Manager (APM) secures and differentiates access to your applications, data, network, and the cloud based on user identity and context. That means it gives you centralized control over who’s able to access your network or cloud, which applications they can access, and the devices and locations from which they can access those apps.

In short, BIG-IP APM unifies and enforces identity-based, context-aware, dynamic policy-driven application access control—regardless of the location of the user or the application

Eg: SSL VPN

APM-Webapplication article link is mentioned below

https://support.f5.com/csp/article/K13425