An EVA is an extravehicular activity or spacewalk in NASA
lingo. The first ten-minute EVA was performed by Soviet cosmonaut Alexei Leonov
on 18 March 1965 when he ventured outside his Voskhod spacecraft
on a tether. American astronauts
developed EVA techniques in the Gemini
program soon after. Walking on the Moon required yet another set of EVA techniques and equipment.
Skylab, the first American space station, got off to a bad start when a large solar panel failed to deploy. The first crew fixed it with a series of EVAs and saved the mission.
Shuttle astronauts commonly perform EVAs to work on equipment in the Shuttle payload bay. Sometimes they even venture away from the Shuttle without a tether, using the MMU (Manned Maneuvering Unit) rocket chair to approach satellites.
Many long EVAs will be required to assemble the new International Space Station over the next few years.