Answer:
Solutions get diluted whenever there is an increase on volume but the number of moles of your substance remains the same. Eg: if I have 1 mole of NaCl in 1000ml, then I add 1000ml of water, then net volume is 2000ml but the number of moles of NaCl present is still 1 so the conc went from 1 mol/L to 0.5 mol/L. It was diluted!