He was referring to the inflation rate. What he was saying was (as far as I understood it), if you safe e.g. $10k now, in e.g. 10years you could not buy as much with it as you could at the time you earned the money. Therefore, you "lose" money (or rather purchasing power) by not using it.
And that's why no one should be sitting on their money...invest it! Keep enough for emergencies (6-12 months of rent/food is the general mantra) in your bank account and put the rest in your IRA/401k and/or non-tax advantaged index funds.
