Platform is like a foundation. It's related to Vehicle's Design. In the automotive industry Platform is really a common word. Which can refer to the underlying structure or architecture of a car. Platform is the foundation of chassis, drivetrain, suspension system, and other fundamental components in a car. For example you can check some sales posts from this CarSell website. 

Types 

Dedicated Platforms is a design made specifically for a single type of vehicle. Like EV-only platforms are Tesla's model vehicles. The Hyundai E-GMP has an Electric Global Modular Platform. 

Modular Platforms for flexible designs. Which can be adaptable to different models and powertrains. For example , we can talk about the Volkswagen MQB platform. 

Shared Platforms mainly used across multiple brands. But it's true that it can be used in the same group of brands. Like Toyota and Subaru sharing e-TNGA platform together for their vehicles. 

Importance 

Knowing details about Platform can reduce development and production costs while the buyer is planning to buy a car. Also its important at the matter of faster production. Especially for new models. At the matter of variety of body styles, including sedans, SUVs, and crossovers knowing Platform can help buyers to choose right one. So to staying in cost-effective era its important to know platforms of any vehicle.