What is an Instructional Delivery Platform?
A platform is typically defined in the generic sense as a raised surface of some type that supports other interacting objects. Within computer and software terminology, a platform can be defined as "A platform is any base of technologies on which other technologies or processes are built". The idea is that the platform is not intended to stand on its own, as its definition includes the support of other technologies or applications.
Given this context, there is a rather extensive Wikipedia entry on learning platforms with some useful definitions included. I have excerpted several below.
A learning platform is an integrated set of interactive online services that provide teachers, learners, parents and others involved in education with information, tools and resources to support and enhance educational delivery and management.
The term learning platform also includes the personal learning environment (PLE)
Description from Becta: A learning platform is a framework of tools that work seamlessly together to deliver a student centric learning experience by unifying educational theory & practice, technology and content. Learning platforms can be described as the next generation of Virtual Learning Environments or Learning Management Systems used by educational institutions. The major difference is that a VLE and LMS is an application, whereas the Learning Platform share characteristics with an Operating System (or CoursePark Platform) where different educational web based applications can be run on the platform.
From: https://mfeldstein.com/what-is-a-learning-platform/