FHIR (Fast Healthcare Interoperability Resources) is an international data standard that defines how health information — a prescription, a lab report, a diagnosis — is structured so different software systems can exchange it consistently, without each vendor inventing its own format.
ABDM uses FHIR as the format for records pushed to a patient's health locker or shared between providers. A prescription that's just a scanned image can't be read by another system automatically; the same prescription structured as a FHIR bundle can be understood, searched and reused by any ABDM-compliant software.
For a clinic, this is mostly invisible — it's a technical requirement the EMR handles. Saaro Health structures prescriptions and reports as FHIR bundles when they're pushed under ABDM, so the clinic doesn't need to think about the format itself.