Difference between WAS/NetWeaver/Enterprise

I have been searching for the answers, but haven't been successful yet.

Could someone pls explain the differences in terms WAS, NetWeaver and Enterprise? If they all represent different SAP systems(versions/technologies), then, what do these systems represent and constitute of?

Weblinks for documentations will be appreciated as well.

Thanks in advance, Rahul

Answer:
The following mean the following to me,

Enterprise - the application layer Enterprise 4.7 110 for example
WAS - the Basis layer of SAP - Wab application server is the direct translation
Netweaver - a broader term meaning to me the web enablement of SAP.

too many links,
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regards,
Chap

Answer:
Well your partly right.

Netweaver - technical (typical SAP) umbrella term for all technical things (new) from SAP, including portals, WAS, BI etc.