Product-agnostic is a description of something that is not associated with a particular commercial product -- such as a specific device or application -- or something that is interoperable with all products of a given type.
Product-agnostic means different things in different contexts. Platform-agnostic or cross-platform software may be specific to one type of device, such as a mobile phone, but runs on any combination of operating system and underlying processor architecture. Device-agnostic software runs on various types of devices, including desktop computers, laptops, tablet PCs and smartphones. Microsoft began promoting device-agnosticism with Windows 10, enabling continuous operations across a user's various devices.
In content marketing, a product-agnostic strategy is more likely to appeal to prospective customers than content that comes off like a sales pitch for the vendor's product. It shouldn't really seem like marketing -- in some cases, in fact, it should only be identifiable as marketing because the advertiser is identified as the content provider.
Product-agnosticism has become increasingly important to deal effectively with ongoing trends such as the expansion of BYOD (bring your own device) and Internet of Things (IoT) environments, which require broad integration and interconnectivity of many different types of devices.