What does -y mean in apt-get -y install command?

I always see commands like this

apt-get -y install 

What is the -y tag for and what is the difference between apt-get install with and without the -y tag?

Solution 1:

From the results of running man apt-get

-y, --yes, --assume-yes
           Automatic yes to prompts; assume "yes" as answer to all prompts and
           run non-interactively. If an undesirable situation, such as
           changing a held package, trying to install a unauthenticated
           package or removing an essential package occurs then apt-get will
           abort. Configuration Item: APT::Get::Assume-Yes.  

If you run an apt-get command without the -y option, you need to answer to all prompts that you get from that command interactively in order for the execution of the command to continue.