What is a Platform?
A platform can mean various things on a computer and on the Internet, in general it means something you can base upon:
1: the target platform of an application or other software refers to components that the software was based on and requires in order to function. These components can be both software and hardware, such as an operating system or CPU architecture.
2: a platform on the web is a website or web application that provides methods for its users to publish on its webpages. All social media websites are also called "platforms," as you can post on them. Similarly, websites like Twitch that allow users to live stream are calling live streaming platforms.
3: platform is also an abstract term to describe an online service that is available through several frontends, such as through a website and through an app for smartphones.