What is the difference between PCI Express 16 & PCI Express x16?

[NeedHelp92]

I have the Dell 0XJ8C4 motherboard and I am planning to buy the GTX 1050 or higher GPU soon. My motherboard have the following expansion slots:
1 x PCI Express 16 (Blue)
1 x PCI Express x16 (wired x 4) (Black)

I wanted to know what is the difference between PCI x16 and PCI 16. Also what does the "wired x4" signify? Any of these slots will be good for the new Nvidia GTX 1050 or above?

Here is the motherboard that I have:
http://www.findlaptopdriver.com/dell-0xj8c4/

Thanks in advance.

 

[BFG-9000]

You use the blue slot for the main graphics card. The CPU only has enough PCIe lanes for that slot and the other, black slot hangs off the chipset*. Both are full length x16 slots but if you look inside the black one you will find most of the pins are missing so it performs the same as a 4x slot (but has the latch at the right place to lock a graphics card)

*Z170 chipset has 20 PCIe lanes but is connected to the CPU by a DMI 3.0 link that's equivalent to only 4 lanes of PCIe 3.0 so there's no reason to give it a full 16 lanes when the bottleneck is elsewhere