In Vue, each component has a reference to its parent component, which can be accessed through this.$parent.
this.$parentCan be used to get the parent instance of the component, which can be used in child components to access the data and methods of the parent component. For example, if the child component needs to access the data of the parent component, you can use this.$parent.someDatato get the data; if the child component needs to call the method of the parent component, you can use this.$parent.someMethod()to call the method.
It should be noted that it is not a good practice to use this.$parent to access the data and methods of the parent component, because it will couple the child component and the parent component together, making the code difficult to maintain and reuse. A better approach is to use props and events to implement communication between components to reduce the coupling between components.
If a component needs to access global data or methods, it can be achieved using Vue's dependency injection feature. Using provide and inject allows the parent component to pass data and methods to the child component without using this.$parentto access the parent component.