A Paint Point is a challenge or an obstacle a potential customer is facing, which your product or service can solve or alleviate the impact of. Pain points are key pieces of information in defining a buyer persona template for your target audience.
For instance a common challenge sales reps face is having to spend time on non-selling activities, that are however, vital to their sales efforts. A product or service that can automated this types of sales-related tasks solves a critical point that many sales reps face.