In this context, deep space is anything not in earth orbit. JPL, for instance, runs the Deep Space Network, which is used to communicate with the Mars rovers, spacecraft orbiting Jupiter, etc. as opposed to the NASA TDRS network which is used to communicate with earth-orbiting satellites.
There are various, competing technical definitions of “deep space” — the ITU defines it as more than 2 million kilometers from earth — but the Deep Space Network, and similar networks operated by other countries, are typically used to communicate with interplanetary spacecraft, and are effective basically anywhere higher than geosynchronous orbit (26,000 miles/42,000 km).
There are various, competing technical definitions of “deep space” — the ITU defines it as more than 2 million kilometers from earth — but the Deep Space Network, and similar networks operated by other countries, are typically used to communicate with interplanetary spacecraft, and are effective basically anywhere higher than geosynchronous orbit (26,000 miles/42,000 km).