Meaning
The server-side part of a software system responsible for data processing, database operations, and core business logic.
Three examples from work
Architecture sync
LeadThe backend will validate the subscription status before issuing an access token.
DevThat prevents any bypass from the client side.
Cross-team coordination
Frontend DevWhen will the backend support multipart file uploads?
Backend DevThe implementation is ready; I'm deploying it to staging this afternoon.
Troubleshooting
DevOpsThe backend CPU usage spiked to ninety percent after the marketing blast.
LeadLet's increase our autoscale cluster capacity immediately.
Can act as a noun ('built in the backend') or adjective ('backend architecture', 'backend engineer'). Contras with 'frontend'.