Synthetic data is data produced by a program or model instead of being collected from real events. It is designed to look and behave like real data in the ways that matter for a task: the same fields and formats, similar distributions, realistic edge cases.
It can be structured (rows of fake transactions), text (sample customer emails, generated with a large language model), documents (invoices with random but valid-looking GSTINs and amounts) or images (product photos rendered from 3D models or produced with a diffusion model).