[OpenWrt Wiki] Mounting Block Devices
https://openwrt.org/docs/techref/block_mount21.05.2020 · Block hotplug consists of three scripts, 10-swap, 20-fsck, and 40-mount. When a block devices is added these scripts are executed in the order listed. So, first the device is checked for being a swap section, or to attempt to mount as swap, if it is not a defined section for swap or mount (this is known as anon_swap or anonymous swap).
[OpenWrt Wiki] Hotplug
https://openwrt.org/docs/guide-user/base-system/hotplug28.07.2021 · Hotplug Procd (the init system and process management daemon) executes scripts located in /etc/hotplug.d/ when certain events happen, like for example when an interface goes up or down, when a new storage drive is detected, or when a button is pressed. It can be very useful with PPPoE connection or in an unstable network, or to use hardware buttons.