CDOM is the total time the house has been on the market since it was originally listed. Here's an example. Let's say the homeowners put their house on the market in September, October, and November for 82 days, then took it off the market over the winter because showings decrease over the winter. In March, they put the home back on the market. On the first day it's listed, the Days On Market (DOM) will show that the home has been for sale 1 day, while the Cumulative Days On Market will show 83 days.
Let's say prospective buyers looks at this house on the first day. If they don't look at the CDOM, they might think that the house has been on the market for only 1 day. If they are considering making an offer, they might think that the house will sell quickly or there might be multiple offers due to the short time on market. If they know that the house was really on the market for 83 CDOM, it may relieve the pressure of making a quick decision.
CDOM information may not be easily available. If you are interested in finding out the CDOM for any house, please feel free to call or e-mail.