As one of the primary authors of the Image Packaging System, I think I can answer this question. I've written about this topic before, so here's a quick summary:
pkg(5), the image packaging system (IPS), is a software delivery system with interaction with a network repository as its primary design goal. Other key ideas are: safe execution for zones and other installation contexts, use of ZFS for efficiency and rollback, preventing the introduction of incorrect or incomplete packages, and efficient use of bandwidth.
SYSV packaging, as others have mentioned (which we generally refer to as SVr4 packaging), is the legacy package management system that was used for the operating system prior to Solaris 11.
With IPS, the most important command is simply 'pkg' -- it is the primary utility for managing any software that is installed on a Solaris 11+ system.
The primary differences between IPS and SVr4 packaging are:
- network-based repository support (no, the support for file retrieval
offered by SVr4 doesn't count)
- safe, deterministic updates
- cryptographically-secure package manifests
- extensive, native integration with ZFS
- extensive dependency management capability (unlike SVr4, IPS has a variety of dependency types) that make it possible to manage sets of packages together
- portable (the glassfish web server historically used IPS as its distribution mechanism on OS X, Linux, and Windows)
You can find more information about it in these blog posts from current and former colleagues of mine:
Observations on Packaging