I would define a variable as anything that has the potential to impact the outcome of a situation. For instance, I leave my house at 8am each day. While I can usually get to work in 30 minutes, there are variables that can come into play that will impact how long it takes to get to work. I might get stuck in traffic because of an accident, or I might run out of gas. These variables will impact the overall outcome, which is "how long it took me to get to work".
A dependent variable is one that is dependent upon the other. In my case, the independent variable is how long it will take me to get to work. The dependent variable is how bad the car accident is and how long it takes to open the road back up in full force.
I think that both variables should be used in research because that's the only way to know the true possibilities