"Overflow" is a termed used in the conference and convention planning world to refer to sleeping rooms that are booked at a 2nd, 3rd, or even 4th hotel - in addition to the headquarter hotel of an event. The headquarter hotel's contracted room block may be full, the hotel may be at capacity, or the hotel simply isn't large enough to accommodate all of the rooms in the first place.
Many contracts are signed with full knowledge that overflow room blocks will be necessary. Citywide conventions are one good example of that. On the other hand, many contracts are signed with the intent to fill the room block and not to exceed it (unless by a handful of rooms). Because planners and executive signers are not fortune tellers, it can come as a surprise for a room block to reach capacity weeks from the event, only to find out that the hotel cannot extend additional sleeping rooms to accommodate the additional guests. It is at this point that a new overflow room block comes into play.
Don't be overwhelmed; you have options. The first order of business is to find out which hotel(s) is closest to your headquarter hotel. From there, reach out to their sales team and negotiate a contract with little to no attrition, as it can be assumed that cancellations at the main hotel will allow for lots of movement up until the first day of the event. Do not wait until your block fills to find overflow options. Do your research on the get-go so you're fully prepared when you run into the issue. Lastly, take good care of your guests by communicating their accommodation and transportation options. The last thing you want is for the overflow to be detrimental to the attendance of your event.
To find the best venues for your meetings, research and send RFPs through the Cvent Supplier Network.