Sterile technique is the set of procedures you'll follow to keep from contaminating your yeast, bacterial, or worm cultures with outside mold spores, random microorganisms, or worst of all a different experimental strain than the one you intend to work with.

A little extra heads up about good sterile technique can save you a lot of trouble in the long run.

Although you can find a few odds and ends by Googling "Sterile Technique", a very good primer is the chapter on sterile technique in At The Bench by Kathy Barker, Chapter 9. There is a copy of this book on the shelf above Mark's desk; if you've never taken a microbiology lab course and are unsure how to take care that your cultures don't become contaminated, read this.
Sterile Technique map

Mark's bench.