Single-event upset (SEU)
Beginner
A particle flips a stored 1 to a 0, or a 0 to a 1. Nothing breaks, but the data is wrong.
Novice
A stored bit, in a memory cell or a flip-flop (a tiny circuit that holds one bit), changes value because a particle struck it. Nothing is damaged, but the data is now wrong.
Expert
Handled by error-correcting codes on memories, TMR or DICE flip-flops on registers, and scrubbing. A single strike can flip several neighboring bits (a multi-bit upset), which defeats simple codes and redundant copies placed close together.
Explained in Space (Industries).