What are: TYPE, TYPES, TYPE-POOL, TYPE-POOLS and type group?
<p>I have found a few resources, but I am not sure if I understand.</p>

<p>Some of the resources I found are:</p>

<p><a href="http://help.sap.com/saphelp_nw70/helpdata/en/fc/eb2ff3358411d1829f0000e829fbfe/content.htm" rel="nofollow noreferrer">http://help.sap.com/saphelp_nw70/helpdata/en/fc/eb2ff3358411d1829f0000e829fbfe/content.htm</a></p>

<p><a href="http://basicsofabap.blogspot.com.tr/2009/04/type-groups.html" rel="nofollow noreferrer">http://basicsofabap.blogspot.com.tr/2009/04/type-groups.html</a></p>

<p><a href="http://scn.sap.com/docs/DOC-32630" rel="nofollow noreferrer">http://scn.sap.com/docs/DOC-32630</a></p>

<p>Could you please help me with the keywords: <code>TYPE</code>, <code>TYPES</code>, <code>TYPE-GROUP</code>, <code>TYPE-POOL</code> ? </p>

<p>Where and why are they used?</p>