The DLD is the central government body for property in Dubai. It maintains the ownership register, issues Title Deeds, charges the 4 percent transfer fee (source: Dubai Land Department, eServices) and settles every ownership transfer, whether off-plan through the Oqood or resale through Form F.
Under the DLD, the Real Estate Regulatory Agency (RERA) acts as the regulatory arm: it registers projects, licenses brokers, supervises developer escrow accounts and approves service charges through the Mollak system. Digital services such as the Dubai REST app and the Rental Index also belong to the DLD.
For a buyer the DLD is the authority that makes a purchase legally binding. Ownership is official only with registration at the DLD and the Title Deed, not with the purchase contract alone.
How a purchase runs through the DLD is explained on our buying property in Dubai page.