Simple question about transistor datasheet Опции

[Sara00]

hello i see the 2n3553 NPN power transistor for rf.
i see these statements

Minimum Gain: 10dB
Efficiency: 50%

what is "Gain: 10dB" meaning?
why they show us the effeciency of transistor?it doesn't related to circuit that we design? for example class A or class C?

Thanks

[SSerge]

what is "Gain: 10dB" meaning?

Gain in dB = 10*log(Pout/Pin)

why they show us the effeciency of transistor?it doesn't related to circuit that we design? for example class A or class C?

they show typical params for typical application (see fig. 6 on page 5):
http://html.alldatasheet.com/html-pdf/1507...5/5/2N3553.html