In a listing, you may sometimes see the acronyms DOMM and DOMP.

Here's what they mean:
DOMM means "Days on Market, Multiple-List" and it's the number of days on the market for that current listing.
DOMP means "Days on Market, Property" and it refers to the entire time the property has been active.

So, for example, let's say a property is listed on January 1, 2007.
On January 31st, the DOMM and DOMP will both say "30" because it's 30 days later.

Now, let's say that the seller decides to use a different listing company on February 1st.
Under this new listing agreement, the DOMM would reset to 1, but the DOMP would not.
The property has to be off the market for 180 days in order for the DOMP to reset to zero.

To sum it up:
the DOMM resets every time there's a new listing number, and DOMP resets when a property has been off the market for 180 days.