JDT Annotation Processing (APT) (org.eclipse.jdt.apt.core) is the plug-in that supports compile-time processing of Java annotations. You should only need to list this plug-in as a dependency if your plug-in is an annotation processor.
For an introduction to working with APT, see Getting Started with APT. For information on how to access APT during command-line builds, see Headless Building With APT.