The term Remnant meaning remaining. Thus remnant media inventory in terms of online advertising means the advertising space that is left unsold and is available to the buyers. In case of online advertising, the advertisers generally have to bid to buy a space so that they can advertise on it and get good traffic to their website. The most useful spaces or the top most spaces are sold off easily but then there are some spaces that remain unsold. This is called as remnant media inventory which is then up for sale at discounted prices.
The remnant media inventory is apt for advertisers who do not have a big advertising budget and would still like to get traffic to their website. The remnant media inventory not only exists for online advertising but in other Media channels as well. For instance, in case of television or radio, the prime time is the most popular time and advertising during this period can turn out to be very expensive and most effective. The remaining time or space is then considered to be remnant media inventory and may be available at a discounted price. You can use the remnant media inventory to advertise your website on a budget and can get traffic through it.