Reword the expanded single pointer definition, tweak pointer input de…

…finition

based on @michael-n-cooper 's feedback, changed the first sentence to be "able to be dropped into the spec in place of the term and still make sense", hopefully.
added the distinction to / mention of multitouch in contrast to single pointer interaction

avoiding repetition, removed the reference to Pointer Events spec from my original PR from the single pointer definiton as that's already covered in the definition for "pointer input", but made sure to make the cross-reference to that from the "single pointer" definition actually a link (which I think gets automagically turned into the correct link to the definiton?)

guidelines/terms/21/pointer-input.html

@@ -6,8 +6,7 @@
    <p>input device that can target a specific coordinate (or set of coordinates) on a screen,
       such as a mouse, pen, or touch contact
    </p>
-
-   <p>See also <a href="https://www.w3.org/TR/pointerevents/#dfn-pointer">Pointer Events pointer definition</a> [[!pointerevents]].
-   </p>
+   <p class="note">See the <a href="https://www.w3.org/TR/pointerevents/#dfn-pointer">Pointer Events
+      definition for "pointer"</a> [[!pointerevents]].</p>
 
 </dd>

guidelines/terms/21/single-pointer.html

@@ -3,8 +3,10 @@
 
    <p class="change">new</p>
 
-   <p>A single pointer operation involves the use of a single <a>pointer input</a>, such as a mouse, or a single finger or stylus on a touchscreen. Single pointer operations include taps and clicks, double-taps and double-clicks, long presses, and dragging.</p>
-   <p>Note: Pointer Events [[!pointerevents]] define a pointer as a hardware agnostic representation of input devices that can target a specific coordinate (or set of coordinates) on a screen, such as a mouse, pen, or touch contact.</p>
+   <p>single <a>pointer input</a>, such as a mouse, or a <em>single</em> finger or pen on a touchscreen</p>
+   <p>Single pointer operations include taps and clicks, double-taps and double-clicks, long presses, swiping,
+      and dragging. In contrast, gestures such as "pinch to zoom" or two-finger swipes are <em>multipoint</em> gestures,
+      as they require two or more pointer inputs - in this case, two fingers on a touchscreen.</p>
 
 </dd>