parallel electric dipole simulation



What is meant by a parallel electric dipole? how does it look like structurally ?

How can I simulate it in FDTD ?

Figure from

Design principles for particle plasmon enhanced solar cells


I am not 100% sure but I am guessing that it could be related to the orientation of the polarization of the dipole. FDTD Solutions allows you to define the orientation of the dipole polarization you want. But I guess the question is that what does the author mean by “parallel” here.