Cardholder data, aka CHD, comes from credit, debit, and prepaid cards bearing the logo of one of the PCI founding card brands. CHD includes the primary account number (PAN) alone or in combination with any of name, expiry date, and a piece of hidden data called a service code. CHD can be in any media format including text or binary data in files and databases, images, and audio. All of these formats need to be protected under PCI.
For clarity, sensitive authentication data has additional restrictions. Truncated cardholder data is not considered cardholder data.
For more see the official PCI Compliance glossary.