What is the difference between active and passive FTP?

Active Mode—The client issues a PORT command to the server signaling that it will “actively” provide an IP and port number to open the Data Connection back to the client.

Passive Mode—The client issues a PASV command to indicate that it will wait “passively” for the server to supply an IP and port number, after which the client will create a Data Connection to the server.

There are lots of good answers above, but this blog post includes some helpful graphics and gives a pretty solid explanation: https://titanftp.com/2018/08/23/what-is-the-difference-between-active-and-passive-ftp/