When we speak about explicit model binding we mean convention based model resolution, you can define how route parameters correspond with models. 99% of the laravel developers use Route Model Binding every day. Implicit Binding is — automatically resolving Eloquent models defined in routes or controller actions whose type-hinted variable names match a route segment name. In case of Explicit Binding everything is clear, because we explicitly bind specific parameter with a model or a closure.
It has two purposes: The main purpose of the middleware is to look for route parameters with the interface and replace them with Eloquent models.