voltage across 2 terminals of diode,transistor

[vamshi1]

when we measure the voltage across  2 terminals of a diode using a multimeter

what does it show ?

similarly with any 2 terminals of transistors

what does these indicate??

 

[audioguru2]

It shows that the diode or transistor's junction is working properly.
When it is forward biased and conducts, then the voltage is about 0.7V and when it is reverse-biased, then it doesn't conduct. The forward voltage changes a little with current and with temperature. When it is very hot then it conducts a little leakage current when reversed biased.