On Fidonet, a FREQ was a File REQuest. A BBS made a file available--most often a FAQ for a specific echo, or some similar file, such as the piece of software the echo was devoted to--and the user sent a properly written Netmail message to that BBS. If the Netmail were sent routed (i.e., the user went through his hub, who went through the zone hub, etc.), the file was returned the same way, uuencoded if binary, and broken into as many chunks as the mailer software found easily digestible. If the Netmail were sent direct (i.e., the user's system directly dialed the system hosting the file), the file was downloaded then and there by the mailer (usually using the ZModem protocol, although others such as the much less used Xmodem, Ymodem, or even the once-ubiquitous Kermit were possible as well).
FREQ's, of course, are much less common nowadays with the rise of the Internet giving access to better methods such as FTP and HTTP, although Fidonet does still exist, albeit in a much reduced form.
Note: This is from memory. Corrections or suggested additions are welcome.