i) Q point: It is the point on the load line which represents the dc current through a transistor (ICQ) and the voltage across it (VCEQ), when no ac signal is applied.
ii) DC load line: The DC Load Line is the locus of all possible operating point.
The DC load represents the desirable combinations of the collector current and the collector-emitter voltage. It is drawn when no signal is given to the input, and the transistor becomes bias.
iii) Need of biasing: As transistor can operate in cutoff, active and saturation. To operate the transistor in respective region, depending on the application for which the transistor is used, it should be correctly biased. So biasing decides the position of operation point on the load line so that the operating region is as desired.
iv) Current Gain: It is a ratio of output current to input current.