CRC (cyclic redundancy check)
A checksum based on polynomial division, designed to catch the kinds of errors that noisy wires and worn flash cells actually produce.
W. Wesley Peterson described the method in 1961. The data is treated as one long binary polynomial and divided by a fixed generator polynomial; the remainder is the checksum. It sounds involved but boils down to a few XORs and shifts in hardware, which is why CRCs are everywhere: Ethernet frames, CAN messages, ZIP and PNG. Plenty of microcontrollers ship a dedicated CRC unit, and a bootloader will often check a firmware image's CRC before jumping into it.
An n-bit CRC catches every single-bit error and every burst up to n bits long. It offers no protection against deliberate tampering, though — anyone can recompute it. That job needs a signature.