A large, general-purpose model trained on broad data that can be adapted to many downstream tasks.
Friendly Description: A foundation model is a big, all-purpose AI that serves as the starting point for lots of other tools. The name fits: it's the foundation, and people build many different applications on top of it. Instead of training a brand new model from scratch every time, developers take a foundation model and adapt it to whatever they need.
Example: Think of a foundation model like a multipurpose kitchen appliance. One company might use it to power a writing assistant, another to build a customer service chatbot, and a third to summarize long videos, all built on top of the same powerful base.