Hi,
to know the meaning of this sentence, I will give you a simple example:
imagine we have a metal sheet of small thickness, you have two options,
1. either to treat it as a box with small thickness, which will give you a lot of unrequired unknowns, but the current would be the same as in the real case (within the accuracy you choose according to number of elements, basis functions, etc .. , of course).
2. you treat it as a zero thickness sheet. in that case the current on one element would be the mean of the two currents, in that case you would get the equivalent problem, which should give a result very near to the actual case, concernming the fields, but not the actual current. i.e. this would be the equivalent case.
hope this might help
best regards,
Adel_48