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You didn't, but should've provided a link to the source of the code you show. I believe it came from the Writing a tf broadcaster in Python.
Translation, in this context, refers to linear movement through space. Transformation refers to the conversion of a position in 3d space (location and orientation) between frames of reference. A transform in ROS represents the position of an object in 3d space at a specific time between two specific frames of reference.
In the case you cite, a fixed elevation (z location coordinate) is given, which happens to be 0. Also, only the theta value (i.e., yaw, rotation around the Z axis) of the Euler orientation changes -- the pitch and roll (rotation around the Y and X axes, respectively) are fixed at 0.
Putting that all together, as the turtle moves in its own frame of reference (i.e., turtlename), its (x,y) location and theta orientation changes (in 2d space on the plane with z=0) relative to the world frame of reference. The sendTransform method enters that information into ROS's TF system with an assigned timestamp.
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