The phrase "reliable backup" means having a trustworthy and dependable copy or support that can be used in case the original or primary option fails. Full definition
But, if you lose the wallet, your bitcoin are gone, unless you have created a clone and / or kept reliable backups of the keys. (coindesk.com)
Has an established reputation for designing reliable backup systems, seamlessly implementing database upgrades and merging database segments without any loss of data. (resume-now.com)
Just be sure to work the transfer into your daily routine in order to maintain it as reliable backup. (lawyerist.com)