Access (control) is the selective restriction of access to a [...] resource. The act of accessing may mean consuming, entering, or using. Permission to access a resource is called authorization.
Within SharePoint.SE there are a lot of questions on the topic Access Denied in various forms, where a user or a group of users are not authorized to access a certain SharePoint resource.
Questions tagged access regards the development, installation, implementation and maintenance of access in SharePoint.
Reference: Access control