1. Software product development targets a broad market with predefined features, whereas custom software development focuses on specific requirements for individual clients.

2. Product development is for mass markets, aiming for wide applicability and scalability, while custom software is tailored to meet the unique needs of a specific client or industry.

3. In product development, the scope is defined by market demand and is often larger, whereas custom development is client-specific with a narrower, client-defined scope.