In a multivibrator circuit, when one transistor conducts, the other is:

A multivibrator circuit (such as an astable, monostable, or bistable oscillator) relies on a cross-coupled configuration of two transistors. The fundamental design dictates that these transistors operate in mutually exclusive states to allow for switching or oscillation. When the first transistor is driven into saturation and is fully conducting, the resulting voltage change at its collector removes the base drive from the second transistor. This forces the second transistor into a non-conducting state, universally referred to as being "cut off". When the circuit transitions, the roles reverse: the cut-off transistor turns on, forcing the previously conducting transistor into cut off.