Levain - This is acctually just a starter that you have activated with fresh flour and water
Starter - The thing in the container consisting of flour and water, and organisms. This is what you keep for your savings and create a levain out of
Feeding: putting fresh flour and water into some starter solution. You can either feed to keep the starter happy, or you can feed to make the levain
Active starter/levain: when our starter is at the peak point of feeding