The dark stripe on credit cards and other ID cards is a magnetic stripe.
This technology is one of our older technologies. It had an advantage of being low cost; however, the cards are easily corrupted and don’t hold up well. Even so, this technology is still in use for credit cards and some id cards and of course on some access control systems.
Recently, certain disreputable characters have developed ways to copy the ID held on the magnetic stripe! So this technology is typically not used in high security application without a PIN code or other secondary method of ID.
Because they are economical, much less expensive than proximity cards, we see these a lot in our daily lives. However, in the access control industry, they are coming into disuse.