Difference between <xs> and <xsd> tags in XML schema file?

What is the difference between the <xs> and <xsd> tags in XML schema files?

From stackoverflow

• from w3.org

  The XML representation of schema components uses a vocabulary identified by the namespace name http://www.w3.org/2001/XMLSchema. For brevity, the text and examples in this specification use the prefix xs: to stand for this namespace; in practice, any prefix can be used.

  in the end xs or xsd are only prefixes. XSD is used for example more by Microsoft schemas.

  The important is how you declare the namespace.

  <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"></xs:schema>
  

  or

  <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"></xsd:schema>
  

  should be equivalent.