Ah, "bitcoin background traces" could be referring to the traceability of bitcoin transactions. Since all transactions are recorded on the public blockchain, they leave a sort of "digital footprint."

You can't see who made a transaction just from looking at the blockchain (since it uses addresses, not names), but you can see when and where bitcoins were sent.

So in that sense, every bitcoin transaction leaves a "trace" in the background - kind of like how every car leaves tracks on a dirt road. It's part of what makes Bitcoin both transparent and secure!