The word usually gets explained in terms of services and databases, which puts the mechanism before the reason. A bounded context is the region within which a word means exactly one thing.
// Sales: a customer is someone who might buy
final class Customer { public $leadScore; public $lastContact; }
// Shipping: a customer is an address and a phone number
final class Customer { public $address; public $phone; }
// Billing: a customer is a legal entity with a VAT number
final class Customer { public $vatNumber; public $creditLimit; }The instinct is to unify them into one class with fifteen fields, most of them irrelevant to any given caller and each one owned by a different part of the business. Three small models with a shared identifier is usually the better answer: each is simple, each changes for one reason, and the translation between them is explicit rather than implied. Where the same word means two things, there is a boundary whether or not it has been drawn.