Form based on Product Types

If you have a seller accounts at amazon or ever happened to look at their product upload form, I am sure you must have noticed that for each product type you wish to upload they have a slightly different form.

If you want to sell Table Fans, you are presented with this form and in case you wish to sell shirts, this is what is presented you. Look at the image down below

both forms are different yet do the same thing, i.e. upload products (which has some common and few specific attributes)

What intrigues me about this design is the thought that the end user, a layman, wouldn't be expected to understand jargon like product attributes or its use. You give him a product specific upload form and he will fill it up as necessary.

Looking at a few other carts, take for instance opencart, opencart has one form for all product types and if you need to add a few extra attributes it lays the onus on you (the end user) to first understand what attributes are then work as needed.

Opencart product upload page

I like the way amazon (and a few other ecommerce site, I believe ebay too does as amazon) worked this up.

I wish to replicate this for my project but honestly speaking I have never seen this before. I do not even understand what do you call this. I tried searching google for "form based on product type" and could not find anything to help me.

Can you please let me know how amazon or ebay do this.