Answer Description

A port scanner can return three things: OPEN, CLOSED and FILTERED. Open means the port is open and accepting connections. Closed means the server responded saying the port is not in use. Filtered means the server sent no response (this is common when a firewall is in front of the server). Based on the information above we only know that port 21 (FTP) is in use.

Wikipedia

A port scanner is an application designed to probe a server or host for open ports. Such an application may be used by administrators to verify security policies of their networks and by attackers to identify network services running on a host and exploit vulnerabilities. A port scan or portscan is a process that sends client requests to a range of server port addresses on a host, with the goal of finding an active port; this is not a nefarious process in and of itself. The majority of uses of a port scan are not attacks, but rather simple probes to determine services available on a remote machine. To portsweep is to scan multiple hosts for a specific listening port. The latter is typically used to search for a specific service, for example, an SQL-based computer worm may portsweep looking for hosts listening on TCP port 1433.