People, Audience, Users, Contacts, Customers

Marketing tools have different ways of referring to the individuals or businesses you have added to the tool for interaction. The most common terms are People, Audience, Users, Contacts, and Customers. They generally refer to the same thing but the choice of the term will depend on the exact function of the marketing tool. Most email marketing tools, for example, use “Contacts”. Marketing analytics tools mostly use “Users”.
Other definitions
Heidi Cohen

For marketing purposes, your audience is broadly defined as anyone your business and/or brand engages with, either directly or indirectly.

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Bitrix24

In most CRM systems, the term contact designates an individual who has purchased your product or service or a company representative responsible for purchasing.

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Investopedia

Customer is an individual or business that purchases another company's goods or services. Customers are important because they drive revenues; without them, businesses cannot continue to exist.

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Get2Growth

Customers are the individuals or organisations who, in some way, actively engage with your business or brand. In the classic sense, this would be a commercial engagement where there is an exchange of monetary value in relation to the delivery of your product or service.

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