Codabar is a linear barcode from the early seventies that encodes digits and six punctuation characters, wrapped in a start and stop letter from A to D. It needs no check digit to be read reliably, which is why it was adopted for printed labels long before scanners were sophisticated.
It is rarely chosen for anything new, but it is far from dead. Library membership cards, blood bank bags, photo processing envelopes and some parcel systems still run on Codabar, and those estates have scanners and back-office systems tuned to it. For a program in that position, keeping the existing Codabar member number is often cheaper than reissuing every identifier.
Like Code 39, Codabar is low density and numeric-only, so it takes width on a pass and cannot carry a rotating token. It suits static membership numbers and nothing more demanding than that.
Google Wallet renders Codabar as a pass barcode. Apple Wallet supports QR, PDF417, Aztec and Code 128 only, so an Apple pass typically carries the same member number as Code 128 or a QR code. QR and barcode identification covers how a program can run both without members noticing the difference.