Big-Oh

On week 8, our professor introduced the concept of Big-Oh. However, I missed Monday's lecture because I went to a wrong classroom. I noticed I was in a statistic class after class began. I was too shy to get out. At least, I understood what that professor said and I thought I learned that kind of things in data management course in  high school. I was smart enough to understand the annotated slides on course website, but I was pretty sure that I missed something on Monday. That might be very important...