Why was the conflict between the US and the Soviet Union called the "Cold War"?

Because, unlike "hot" wars, a "cold" war features relatively little direct military conflict. The US and Soviet Union never fought directly on each other's native soil, but instead conflicted via policies, diplomatics, embargoes, and the occasional "offsite" military confrontation (e.g. Korea and Vietnam).

Hot wars contain shooting, a Cold War does not. The war with the soviet union almost escalated to a hot war several times, but fortunately did not.

Because it was all politics...

"The struggle was widely called the Cold War in that it did not involve direct armed conflict between the main contestants (by contrast, a so-called "hot" war). The Cold War was instead waged by means of diplomatic maneuvering, economic pressure, selective aid, intimidation, propaganda, assassination, low-intensity military operations and full-scale proxy wars."

I agree with kavin exact devination cold war means what he said.