Firewall (definition)

Some organizations separate their networks from the rest of the Internet by installing a "firewall" or "gateway." A firewall is a system or software which is configured to prevent particular types of access/information from entering the network. Most firewalls block the flow into the local area network, but allow individuals to access most resources outside of the network.

Some types of router-based firewalls will not allow an FTP site to establish a data connection to your local PC. You will want to use passive transfers if your local area network is behind these types of firewalls.