What's an "inline query"?
In the FROM clause below, the subquery acts as a table:

SELECT * FROM (SELECT id, name FROM users)


That subquery is called an inline view. So in this case you are not directly selecting rows from a table, but from an "inline view".
 From your first link it seems that the user created an actual view, which you can do from a query. More information over here: https://www.postgresql.org/docs/9.2/static/sql-createview.html

But it seems that Erwin thinks it might be a better idea, performance wise in that specific case, to "inline the query" from the view. Or in other words, not by first creating a view but use inline views like I did.

Hope this helps.