There are several types of PIM, but the most common is probably product information management. This is a system for organizing and storing product data, which can include things like product descriptions, pricing information, images, and more. This data is typically used in ecommerce platforms, so that customers can easily find and purchase products.
PIM systems can vary in terms of features and complexity, but most will allow you to import and export data, manage multiple languages and currencies, and setup workflows for things like approvals and publishing. Some more advanced PIMs may also offer things like analytics and reporting, customer segmentation, and product recommendation engines.