Refer to %p in the psql docs as 'process ID' not 'pid'.

Per Tom.

doc/src/sgml/ref/psql-ref.sgml

@@ -3367,7 +3367,7 @@ testdb=&gt; <userinput>INSERT INTO my_table VALUES (:'content');</userinput>
       <varlistentry>
         <term><literal>%p</literal></term>
         <listitem>
-         <para>The pid of the backend currently connected to.</para>
+         <para>The process ID of the backend currently connected to.</para>
         </listitem>
       </varlistentry>