The document discusses how Davey's interests in cycling are tracked across devices by advertisers and data management platforms (DMPs) using cookies. Davey's cookie collects information about his interests, like cycling, and demographic details, like being a male in his 30s. This allows advertisers to target Davey with cycling products. When Davey visits websites that work with DMPs, he is shown an advertisement for a new product from Switchbikesaregreat.com based on matching his cookie data. DMPs also help publishers and advertisers identify other users similar to Davey to help advertising campaigns reach more potential customers.