Does taxiing time gets considered in a pilot's flying hours?
In the US, taxi time can be logged. 14 CFR 61.51 says the pilot must log (emphasis mine):


  Total flight time or lesson time.


And 14 CFR 1.1 says (emphasis mine):


  Flight time means:
  
  (1) Pilot time that commences when an aircraft moves under its own
  power for the purpose of flight and ends when the aircraft comes to
  rest after landing; or
  
  (2) For a glider without self-launch capability, pilot time that
  commences when the glider is towed for the purpose of flight and ends
  when the glider comes to rest after landing.


Note that in reality, general aviation pilots (I don't know about airline pilots) usually just log whatever is on the Hobbs meter, which may include some time sitting still on the ramp doing post-startup checks, setting up avionics etc. That might not be strictly correct per the regulations, but absolutely no one cares.

This question is closely related.