An agent fee is the commission paid for negotiating a transfer or a contract, calculated as a percentage of the fee or the player's wages. It is usually paid by the buying club rather than the player, and English football publishes the totals each club pays every year.
The practical reason clubs pay is tax and cash flow. A player would have to earn the money, be taxed on it and then pay the agent; a club paying the agent directly is cheaper for everyone involved, which is how a service bought by the player came to be funded by the clubs.
FIFA brought in a licensing system for agents in 2023, along with a cap on commission as a share of the deal. The cap has been challenged in national courts and before competition regulators in several countries, so how strictly it applies has varied by jurisdiction rather than settling into one global rule.
The published English figures are worth reading with care. They cover a full season across every deal a club did, including contract renewals, so a single large number says little about any one transfer. They are still the only routine public disclosure of what this part of the market costs.