A top-level or "independent" object is one that does not belong to a parent object. For example, Jobs, Job Groups, and Messaging Service Providers are all top-level objects.
By contrast a dependent object is one that always belongs to a parent: Job Steps, Responses, etc.
Independent objects can be saved/deleted and have security settings. Dependent objects are only saved as part of their parent object.
System.Object
ArcanaDevelopment.adTempus.Client.ObjectBase
ArcanaDevelopment.adTempus.Client.ADTObject
ArcanaDevelopment.adTempus.Client.ADTIndependentObject
ArcanaDevelopment.adTempus.Client.AlertNotificationRule
ArcanaDevelopment.adTempus.Client.CredentialProfile
ArcanaDevelopment.adTempus.Client.ExclusionPeriod
ArcanaDevelopment.adTempus.Client.FileServiceProvider
ArcanaDevelopment.adTempus.Client.Job
ArcanaDevelopment.adTempus.Client.JobGroup
ArcanaDevelopment.adTempus.Client.JobQueue
ArcanaDevelopment.adTempus.Client.MessagingServiceProvider
ArcanaDevelopment.adTempus.Client.NotificationRecipient
ArcanaDevelopment.adTempus.Client.RemoteAgent
ArcanaDevelopment.adTempus.Client.Script
ArcanaDevelopment.adTempus.Client.ScriptLibrary
ArcanaDevelopment.adTempus.Client.SecurityEntity
ArcanaDevelopment.adTempus.Client.SecurityTemplate
ArcanaDevelopment.adTempus.Client.ServerSettings
ArcanaDevelopment.adTempus.Client.SharedSchedule