It all depends on the MLS to which the agent belongs.
There are different stages of the selling process, but basically it is Active (on the market), Pending/Under Contract and Sold/Closed. One MLS might use DOM (Days on Market) and another use DSL (Days Since Listed) to differentiate the different status reports.
It is possible for a house to be listed and an offer accepted by the seller the same day. Depending upon the state, a contract could be signed three days later and all the contingencies satisfied 45 days later and the closing held 15 days after that. Would one say that the DOM was 60 days since that is when the escrow closed? Perhaps, but the actual agreement was signed 3 days after the house came to market. Therefore the real DOM was 3 days, not 60.
It may seem like a minor point, but in fact it is important to note because it affects the absorption rate statistics in the market which show if we are in a buyers or a sellers market.