I have an application which is packaged as a single ear file deployed on WebSphere. Inside the package, the code is organized in to UI files, Business Logic files and Database related files. Now, is this a monolithic application or a 3-tier architecture?
What is the difference?
You are comparing wrong things. Monolithic application need to be compared against Micro Services. In monolithic application; you deploy all the features/api end-points in a single EAR/WAR file; i.e. single JVM. In micro-services they are deployed in multiple JVMs. Note that in Monolithic architecture also you have multiple REST end points exposed.
3 tier, or 2 tier or N tier architectures is a different concept. It says how many subsystems/modules your application is divided like database layer, client layer, application logic layer. Hence, monolithic as well microservices both can be n tier applications.