What is sourced traffic?
Sourced traffic is website traffic that a publisher buys from third parties, such as ad networks, content-recommendation widgets, social ads or traffic vendors, rather than earning it organically. It is not inherently bad, since many publishers promote articles, but cheap sourced traffic is a leading source of bots and low-attention visitors, and it underpins arbitrage and MFA sites.
Publishers buy sourced traffic to grow audiences quickly or to run traffic arbitrage: pay a few cents per visit, then show enough ads to earn more than that. Reputable sources such as search and social ads deliver real people; the cheapest vendors frequently mix in bot traffic or incentivized traffic.
For buyers, the risk is paying premium prices for visitors who never intended to read the page. Ask sellers what share of traffic is sourced, check for spikes aligned with paid campaigns, and use quality measurement that flags sourced sessions. Heavily sourced sites with many ads per page are the core of the made-for-advertising sites problem.