Difference between "Referee-reviewed articles" and "Referee-reviewed conference contributions"?

I'm a new PhD student. The specific demands on me are for me to agree to do the following, during my PhD:

1. 
   

   Publish two Referee-reviewed articles and

   
   


2. 
   

   Publish four Referee-reviewed conference contributions

   
   

I completely understand what is 2.

However, I'm not sure what is 1. (but is not 2.).

So my only question is, what is the difference between 1. and 2.?

Thanks!!! Todd