The terms inferior and superior conjunctions refer specifically to the alignment of the Sun, Earth, and either of the inferior planets, Mercury and Venus.
At some point, all three line up in a row, sometimes with the Sun in the middle and sometimes with the inferior planet in the middle.
When the Sun is in the middle, the inferior planet is at superior conjunction and can’t be seen from Earth.
When the inferior planet is in the middle, it is at inferior conjunction.
A conjunction is also sometimes known as an appulse.