Definitions for outer space
Random House Webster's College Dictionary
space beyond the atmosphere of the earth.
Ref: deep space.
Origin of outer space:
outer space, space(noun)
any location outside the Earth's atmosphere
"the astronauts walked in outer space without a tether"; "the first major milestone in space exploration was in 1957, when the USSR's Sputnik 1 orbited the Earth"
Kernerman English Learner's Dictionary
outer space(noun)ˈaʊ tər
anything beyond Earth's atmosphere
a new spacecraft traveling into outer space
Region outside explored space.
Any region of space beyond limits determined with reference to boundaries of a celestial system or body, especially the region of space immediately beyond Earth's atmosphere
Origin: From outer + space.