What is a resource in simple terms?

Question

I know how to use a resource, but I'm not sure what it is. All I understand is that I put in in my XML file and it makes my application work. Can someone explain in simple terms what it is I'm doing when I put it in my XML file?

    <resources>
        <complexworld_setup>
            <setup>
                <module>Magentotutorial_Complexworld</module>
                <class>Magentotutorial_Complexworld_Model_Resource_Setup</class>
            </setup>
        </complexworld_setup>
    </resources>

and

    <complexworld_resource>
        <class>Magentotutorial_Complexworld_Model_Resource</class>
        <entities>
            <eavblogpost>
                <table>eavblog_posts</table>
            </eavblogpost>
        </entities>
    </complexworld_resource>