Modular software is designed as independent modules (e.g. HR, CRM, inventory, purchasing, finance), and your business uses only the modules it needs. All modules run on one integrated platform; new modules can be added when required.
Advantages: You pay only for the modules you need at the start; as you grow, you add modules and expand. Cost scales with use and you avoid complexity from unused features.
Integration: Data is shared between modules on one platform. For example, a sales order reduces stock and a purchase order increases it; the employee list in HR feeds shift and payroll. This reduces data duplication and inconsistency.