Trying to define tenkara is like trying to define the color blue. You might think "but we all know what blue is." The problem is in defining, precisely, just where is the dividing line when a color is no longer blue and is now green. And to make the analogy even more appropriate, the Japanese place that dividing line in a different place than we do in America. Our "green" traffic lights and interstate highway signs fall into the part of the color spectrum that the Japanese call "blue."

What is tenkara? That depends entirely on who you ask.
What is a tenkara rod? That also depends on who you ask (and what he has to sell you).