What does this mean

Solution
Why not go with Skylake instead? Just swapped out the cpu, motherboard, and ram from your build:

PCPartPicker part list: http://uk.pcpartpicker.com/list/VDmcCy
Price breakdown by merchant: http://uk.pcpartpicker.com/list/VDmcCy/by_merchant/

CPU: Intel Core i3-6100 3.7GHz Dual-Core Processor (£94.32 @ CCL Computers)
Motherboard: ASRock B150M Pro4S Micro ATX LGA1151 Motherboard (£58.23 @ Amazon UK)
Memory: Kingston HyperX Fury Black 8GB (2 x 4GB) DDR4-2133 Memory (£28.96 @ More Computers)
Storage: Western Digital Caviar Blue 320GB 3.5" 7200RPM Internal Hard Drive (£19.50 @ Amazon UK)
Video Card: Asus GeForce GTX 750 Ti 2GB Video Card (£99.99 @ Amazon UK)
Case: CiT VANQUISH RED ATX Mid Tower Case (£37.49 @ Amazon UK)
Power...
It means that some H81 chipset motherboards may need a BIOS update prior to using Haswell Refresh CPUs.

Some H81 chipset MB's need a bios update to support the Haswell Refresh CPUs.

If you get one of these MB's you would have to update the bios before you could use the Haswell Refresh CPUs.
 
If you are not familiar with BIOS, don't update it.
This is called "flashing" the BIOS, and it is a risky procedure, because you can end up with a bricked PC.
Better to choose parts that are compatible out of the box.
I am all thumbs, and have flashed my BIOS many times, but that doesn't mean you have to be reckless like me.
 
Why not go with Skylake instead? Just swapped out the cpu, motherboard, and ram from your build:

PCPartPicker part list: http://uk.pcpartpicker.com/list/VDmcCy
Price breakdown by merchant: http://uk.pcpartpicker.com/list/VDmcCy/by_merchant/

CPU: Intel Core i3-6100 3.7GHz Dual-Core Processor (£94.32 @ CCL Computers)
Motherboard: ASRock B150M Pro4S Micro ATX LGA1151 Motherboard (£58.23 @ Amazon UK)
Memory: Kingston HyperX Fury Black 8GB (2 x 4GB) DDR4-2133 Memory (£28.96 @ More Computers)
Storage: Western Digital Caviar Blue 320GB 3.5" 7200RPM Internal Hard Drive (£19.50 @ Amazon UK)
Video Card: Asus GeForce GTX 750 Ti 2GB Video Card (£99.99 @ Amazon UK)
Case: CiT VANQUISH RED ATX Mid Tower Case (£37.49 @ Amazon UK)
Power Supply: XFX TS 430W 80+ Bronze Certified ATX Power Supply (£33.76 @ CCL Computers)
Optical Drive: LG WH16NS40 Blu-Ray/DVD/CD Writer
Operating System: Microsoft Windows 7 Professional Full 32/64-bit
Wireless Network Adapter: TP-Link Archer T4U USB 3.0 802.11a/b/g/n/ac Wi-Fi Adapter (£19.99 @ Amazon UK)
Total: £392.24
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2016-06-02 17:28 BST+0100

http://uk.pcpartpicker.com/list/VDmcCy
 
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