The difference between an Ideal Customer Profiles (ICP) and a buyer persona is that ICPs identify the best-fit customer for a business as a whole whereas buyer personas focus on those individual customers within that ICP framework.
Think of an ICP as a blueprint that provides a high-level overview of an ideal customer, which may encompass multiple buyer personas.
Buyer personas detail the characteristics of different types of individuals under the umbrella of your ICP.
In other words, ICPs zoom out of your ideal customer. Customer personas zoom in.
ICPs and buyer personas complement each other. When these critical components are used together, you can get a focus your sales and marketing effort on broad common customer attributes and address specific customer needs at the same time.