Spaceflight (or space flight) applies astronautics to fly spacecraft into or through outer space, either with or without humans on board. Most spaceflight is uncrewed and conducted mainly with spacecraft such as satellites in orbit around Earth and includes space probes for flights beyond Earth orbit. Such spaceflight operates either by telerobotic or autonomous control.
Splashdown is the method of landing a spacecraft by parachute in a body of water. It was used by crewed American spacecraft prior to the Space Shuttle program, by SpaceX Dragon and Dragon 2 capsules, and is planned for use by the upcoming Orion Multipurpose Crew Vehicle. It is also possible for the Russian Soyuz spacecraft to land in water, though this is only a contingency. The only example of an unintentional crewed splashdown in Soviet history is the Soyuz 23 landing.
As the name suggests, the capsule parachutes into an ocean or other large body of water. The properties of water cushion the spacecraft enough that there is no need for a braking rocket to slow the final descent as is the case with Russian and Chinese crewed space capsules (while Shenzhou designed a raft and balanced capsule in case of splashdown), which return to Earth over land. The American practice came in part because American launch sites are on the coastline and launch primarily over water.