The owners that have lost the keys are actually out of circulation at this time but anytime they remember the password the coins can be back into circulation and increase the supply so there is difference in these terms.As per report there are over 4 million coins lost but actually they have not the password and keys with them.
This is not an accurate statement. There are plenty of reasons that coins might not move for 5 years or more that do not include the owner losing the keys.
The actual coins lost are the one's which are send to OP_Return command as they can't be retrieved at all and are out of circulation.
There are actually a few other ways that coins have been provably lost, which I have previously outlined
here and
here. Still, the number of provably lost coins is in the region of 2,823 BTC, and certainly nowhere near the 4 million that some people speculated.