To get the answer of that question, we need to take a look at the global architecture of an Eclipse-RCP-based application. This picture below can summarize the information.
SWT is Standard Widget Toolkit for Java. Developed by IBM and later by Eclipse Foundation, the purpose of SWT is to give native performance and look to Java application. SWT is implemented using JNI and so is not write-once-run-anywhere-library (WORA). This mean that each OS need specific SWT distribution.
JFaces is a layer above SWT which provides more convenience classes for generic application. JFaces is a WORA library.
OSGi is a standard developed by consortium with the same name to provide Java environment that is more dynamic. The goal is extensible, loosely-coupled applications with modules behind it.
Equinox is Eclipse implementation of OSGi.
Eclipse Core and Eclipse UI are classes that form the platform of Eclipse. All Eclipse-RCP-based applications will use this classes. Among other things, it provides extension framework, command framework (and somewhat-deprecated Action framework), and basic application-window management.