A wet dress rehearsal (WDR) is a critical pre-launch test for rockets and spacecraft. During a WDR, the launch vehicle is loaded with propellants and all countdown procedures are executed up to, but not including, engine ignition. This process allows engineers to simulate actual launch conditions, test ground support equipment, and identify potential issues under realistic scenarios. The term 'wet' refers to the use of real, cryogenic propellants, as opposed to 'dry' runs that do not involve fueling. WDRs are essential for ensuring safety and mission success by verifying that all systems function correctly when fully loaded and pressurized, minimizing the risk of failure during the actual launch.