FTP is an abbreviation of File Transfer Protocol which is a way to transfer files over the internet. Usually ftp is used to transfer files from your computer to online directory like your WordPress web hosting server.
Back in the days, using ftp was the most popular method to transfer even large files but the advancement of technology and internet speed makes it less popular now. Its also because other more robust options are available to internet users now a days like websites offering to transfer large files, dropbox, onedrive and other well-known options.
See our article on how to setup an ftp account to be used with WordPress or any other blogging platform.