In Active Mode, the FTP/S server initiates the data channel connection to the client port specified by the client-issued PORT command given when first connecting to the server via the command channel. This mode is rarely used anymore and can only work if the client isn’t operating behind a firewall. Passive Mode is the opposite, meaning the FTP/S client initiates the data channel connection to the server port specified by the FTP/S server in response to the client’s PASV command. This mode is more common and allows a client to connect to an FTP/S server behind a firewall.
Read about the differences between Active and Passive FTP/S