"OTL", sometimes seen as Or2, On_, on_, OTZ, orz, O7Z, ○| ̄|_, or (in backward) Sto, Jto, illustrates a person facing left and kneeling on the ground, especially out of discouragement.
push pull refers to Class B output. Advantage of Class B is power saving, when there is no input there is no power dissipated in the output, disadvantage is distortion when signal is at low level (near zero crossing). There are techniques to correct them, nonetheless additional components are involved so it's better to use Class A to maximum quality output.
single ended in general means an input with a singal level in reference to (usually) ground. The opposite is differential input, which has higher common noise rejection.
A triode is a type of vacuum tube with three elements, I don't know much about them since they are largely obsolete except in audio.
Et cetera, usually abbreviated to etc. (archaic abbreviations include &c. and &/c.) is Latin for and the others