The above use of the terms "open" and "closed" can sometimes be misleading, though; it blurs the distinction between a given port being reachable (unfiltered) and whether there is an application actually listening on that port. Technically, a given port being "open" (in this context, reachable) is not enough for a communication channel to be established.
The terms "open" and "closed" can sometimes be misleading when describing ports; they don't always accurately reflect whether an application is actively listening on that port.  Simply being accessible doesn't guarantee a connection.