To the non-rclone users, this refers to one of the targets of rclone; the crypt backend wraps the real backend by chaining them together, e.g. localdata <=> crypt <=> providerstorage (basically like a bi-directional filter). https://rclone.org/crypt/

Edit: I use rclone as the backend for duplicity, so you can also chain it through another tool with different encryption and use rclone as just the transfer engine, getting all the benefits of rclone's providers with the benefits of duplicity's backup strategies.