The Serviceable Obtainable Market refers to the group of customers who you could realistically gain business from. While you may identify a target market in the form of a Serviceable Addressable Market or SAM, the SOM is only a percentage of the SAM.
For example…
Country-based organic farmer, Linda has decided to personally sell some of her produce at the city’s farmers markets every month. Her Serviceable Addressable Market is all those people who attend the farmers market but her Serviceable Obtainable Market will be a fraction of the SAM as not all of the market will visit her shop.