#1: Science is a changing and growing collection of knowledge, characterized by transparency (all methods are documented, and the lineage of ideas can be traced) and testability (prior work can be repeated or its results evaluated). It is an edifice of information that contains all of the details of its construction.
#2: Science is what scientists do. We have institutions that train people and employ them in the business of generating new knowledge — contributing to that edifice in definition #1 — and we have procedures like the bestowal of degrees and ranks that certify one's membership in the hallowed ranks of science.
#3: Science is a process. It is a method for exploring the natural world by making observations, drawing inferences, and testing those inferences with further experimentation and observation. It isn't so much the data generated as it is a way of thinking critically about the universe and our own interpretations of it.
There are essentially three different usages of the word "Science" that I have seen, and Pharyngula neatly sums them all up. #1 is the layman's definition, #2 is the research scientist's, and #3 is the educator's. When I student-taught middle school science, one of our main goals was showing the kids that they ARE scientsts themselves and that they already do use the process of science in their everyday lives, so it's not something big and scary and separate from them.