Gets a Boolean value that indicates whether the field derives from a base field type.
Assembly: Microsoft.SharePoint (in Microsoft.SharePoint.dll)
Available in Sandboxed Solutions: Yes
Available in SharePoint Online
The base field types are defined in FLDTYPES.XML, which defines the default schema for lists. Every built-in list in a site inherits its schema from a base type. If the FromBaseType property returns true, the field cannot be converted to another field type, nor can it be deleted.
If you want to prevent a field from being modified or deleted, set the Sealed property to true.