What does it mean when it says Avast is buildiing a database to protect you

Avast Free Antivirus / Premium Security
1

HI I was wondering if I could ask a question. When you get to the end of installing avast 8 free a screen pop up comes up saying that avast is installed on your computer and that avast is building a database to protect your computer. I think that is the correcting wording. Not a hundred percent sure though

What I would like to now is what does this mean exactly.

thanks for the help

2

guessing it is checking installed files with a online database of safe files