A coil measures 25 cm x 15 cm & is 20 cm long...

when annotating the dimensions of an object, i always specify what's what.
ie. 25cmW x 15cmH x 20cmD

W = width
H = height
D = depth

"long" refers to it's width, so the other two dimensions would be height and depth.
without seeing the coil, it's impossible to know which is which.

if it's a circular coil, the height and depth (by definition) would be equal...

Although you may have a different opinion, I wouldn't even hesitate on that one.

According to RP statement, the two first measures would be width x height and the other being the length :

(sorry for the typos on the picture)

agreed if you substitute depth for length...

For practical purposes, I cannot agree.

It's always the length of a coil, not the depth, around here.

We use the depth for the measure of something that is perpendicular to the plan of your eyes.

Long coils are almost always placed parallel to the plan of your eyes..

But it's only around here, maybe...

(one could argue that the length of a coil would be it's measurement uncoiled...)

You say "long refers to it's width but I suggest it refers to it's length.

As to the other two measurements, it's understood that width and height are equal if the coil is round, given the diameter is the same from any angle. It’s not likely round although it could be oval or rectangular or some other asymmetrical shape.

If it was round (unlikely) it’s understood it would make no difference which of the remaining measurements are width and which height as that would simply be a case of orientation and would not affect the magnetomotive force calculations associated with the coil.

Well maybe yes and maybe no because it could be oval, or rectangular or some other asymmetrical shape.

Specifically to your photo, it is not actually rectangular. It's understood in coil construction that the bobbin is not likely to have 90 degree angles (and your photo demonstrates this) so this rounding of angles means that the cross sectional area cannot be assessed accurately by L x W.

No that would be length of the wire not the length of the coil.

Sure, I'm good on that but it does not change the fact that it could be oval, or rectangular or some other asymmetrical shape nor does it change the fact that it's not truly rectangular from the perspective of its cross sectional area and thus any calculations based on magnetomotive force, etc.

i am drawing from my experience in the engineering biz.
as the diagram i posted shows, width is the measurement of the front face of the object.

i have no knowledge of how coils are dimensioned...

The silly thing about it all is I have to invilgetle an exam next week on magnetism and the question (in part) contains the text I referenced. Even sillier is that it turns out the two unknown dimensions are basically a red herring as they are not required to solve for ampere-turns...well this I discovered by calculating the answer while ignoring the two unknown dimensions because:
a) I can see no way to accurately assess the two unknown dimensions in terms of cross sectional area of the coil.
b) after noodling with the question for a spell, it become obvious the two unknown dimensions (and thus the cross sectional area of the coil) were not needed to solve.

Any-who I thought it might be interesting to see if anyone could precisely assess what the two dimensions are a function of...but this appears unlikely.

invigilate