Question What is this phenomenon called when this happens to a motherboard or any other PC component / electronics?

[Lolcocks Lolcocks]

So I have an ASUS Strix Z270F and it was used from a little less than a year.

On the back of the motherboard there is some sort of oil accumulation on the plastic but it's not exactly oil and doesn't come off.

https://i.ibb.co/8Dcqyfr/IMG-20190408-214127-Copy.jpg

What is this phenomenon called?

EDIT:
Actually on the other side of the board there are power MOSFETs which tend to heat up a lot. So much so that they have their own heatsink.
I am guessing what has occurred is because of heating.

Still, I would like to know what this phenomenon is called.

 

[Deleted member 14196]

it looks burned.

 

[Lolcocks Lolcocks]

it looks burned.

It's not burnt mate, all the devices I saw this on are working fine, include that motherboard I posted.
My own motherboard has this since three years, it's working fine.

 

[Lolcocks Lolcocks]

it looks burned.

Actually on the other side of the board there are power MOSFETs which tend to heat up a lot. So much so that they have their own heatsink.
I am guessing what has occurred is because of heating.

Still, I would like to know what this phenomenon is called.