In short
Serialisation is the practice of assigning a unique identifier (serial number, 2D code, etc.) to each unit of product so it can be tracked at unit level.
Batch traceability follows a group of products together, while serialisation follows individual units. This matters for anti-counterfeiting and for verification along the supply chain.
In pharma, 2D-code-based serialisation is a regulatory requirement in many countries. Serialisation is usually implemented together with aggregation at case and pallet level.