SDLC is a catch-all or umbrella (dending on whether you turn it up or down I guess) for all the things you do in a project. There is a pretty perky industry around books and tools that help you understand and remember all the right steps. Of course, no two of them list exactly the same steps, but they'll all talk about things like starting the project with a good understanding of what everyone expects from it, learning the details about what it should do, designing, coding,
testing, deploying, running the system, shutting it down when it becomes obsolete. They might get heavily into how to plan and manage or how to design and code.
Rational Unified Process (RUP) is probably the best known process today. You can use it in many different ways so it's pretty hard to pin down just what it's like.
If you scan this forum you'll find us mostly interested in the "Agile" movement toward processes that focus on delivering running software instead of producing documents and passing through process gates. These processes run requirements gathering, design, coding and testing on very small chunks of software in short iterations so you can't say things like "We're in the design phase of the project now"
For a taste of what agile stuff is about, try
XProgramming.com or
ExtremeProgramming.org. I'm sure the gang here will jump in with more recommendations for books and sites.
