Explain - Lock Fuse: 3F is FFailed to verify fuses

Trying to re-programming a Pro Trinket boot loader I get the message:-
“Lock Fuse: 3F is FFailed to verify fuses”.
As a beginner what are these “fuses” (to me they are bits of wire that protect circuits from overloads!) and does this message mean that the Pro-Trinket is now useless? (i.e. cannot be fixed).The re-programming of the device was undertaken because trying to download a sketch to the device caused an error:-
“An error occurred while uploading the sketch
avrdude: verification error, first mismatch at byte 0x0042
0xf0 != 0x4b
avrdude: verification error; content mismatch”
I look forward to a simple explanation!
Thanks in advance

For an explanation, the fuses set the chip configuration, like clock source, frequency, bootloader etc.

Trying to reprogramming the bootloader unsuccessfully, you've probably destroyed previous one so no wonder it doesn't work anymore. You have to upload the bootloader again. Be sure your bootloading circuit is correct. Post the full log from upload.

Thank you for your reply - apologies for delay in thanking you. I followed the instruction in the Adafruit document "Introducing ProTrinket" so the circuit and procedure should be correct, thus I suspect that the chip has been damaged.

Thank you again, DT