"DOM" on an MLSi stands for "Days on Market". Day 1 would be the day the listing was taken by the Realtor. Some area MLS's (including the Phoenix metro MLS) split up DOM into "CDOM" or Cumulative Days on Market, and "ADOM" meaning Agent Days on Market.

Most MLS's that use CDOM and ADOM work like this:

Day 1 for CDOM is the day the Realtor takes the listing. ADOM and CDOM are the same, unless the seller changes agents. If that happens, ADOM resets to 1, but CDOM keeps running.

Say a seller uses agent Joe for 10 days, and then switches to Agent Sue and Sue has listed the house for 18 days. Then CDOM = 28, and ADOM = 18. Make sense?

*Generally* speaking, newer listings (lower DOM) get more activity as interest tends to be higher when a home is first listed. The average DOM is a good indicator of market activity. Shorter average DOM means the area is in a seller's market and longer DOM means it's a buyer's market. It's important to understand that DOM stats really only apply to a local market. You can't (or shouldn't) compare average DOM in Phoenix to say average DOM in Dallas. Real estate markets are driven by local conditions and situations far more than most people realize.. And different MLS's have different rules and regulations on how long a home has to be off the market before the DOM resets to zero (good rules in this area prevent people from "cheating" and artificially making their listings appear new).