Question

Why were the states which surrounded the USSR known as "satellite" states?

Answer 1

I think because of their political and economical dependence from the USSR that, like a big planet, kept the smaller one tied in its orbit (exactly as satellites around a planet).

Explanation:

In particular after WWII USSR imposed the forming of communist governments and, in doing so, basically ruled some states (theoretically independent but in reality under the direct control of USSR) such as:

The People's Socialist Republic of Albania
The Polish People's Republic
The People's Republic of Bulgaria
The People's Republic of Romania
The Czechoslovak Socialist Republic
The German Democratic Republic
The Hungarian People's Republic

You can see this type of direct control and influence during the Prague's insurgence (Prague Spring) when USSR sent tanks to crush the revolt and to establish a pro-USSR government.