In Ubuntu 18.04 LTS and above
suspend-then-hibernate works similarly
In this mode laptop sleeps or suspends to RAM when the lid is closed of a button is pressed. After a certain time that has been pre-set, the laptop will wake up and write the data in RAM to disk, and enter hibernate mode.
The advantage is, the laptop suspends (sleeps) more quickly when close the lid. If you wake it up before the pre-set time it resumes quickly as well. If you don't wake the it up before the pre-set time it automatically saves battery in hibernate mode shut-down.
In Ubuntu 17.10 and below
hybrid-sleep was the closest
In this mode the data in RAM is written to disk for hibernating before the laptop entered sleep (also known as suspend) mode. If the battery gets critically low while sleeping, the laptop goes into hibernation before turning off power, so the data in RAM is not lost.
In case the battery is drained out while the laptop was in hybrid sleep mode, plugging it into the power socket and powering it up will bring it back to the state when the lid was closed to put the laptop to sleep.
See What is hybrid suspend for some more explanations.
From the Ubuntu manpage on systemd power-saving mode:
systemd supports four general power-saving modes:
a low-power state where execution of the OS is paused, and complete power loss might
result in lost data, and which is fast to enter and exit. This corresponds to suspend,
standby, or freeze states as understood by the kernel.
a low-power state where execution of the OS is paused, and complete power loss does
not result in lost data, and which might be slow to enter and exit. This corresponds
to the hibernation as understood by the kernel.
a low-power state where execution of the OS is paused, which might be slow to enter,
and on complete power loss does not result in lost data but might be slower to exit in
that case. This mode is called suspend-to-both by the kernel.
A low power state where the system is initially suspended (the state is stored in
RAM). If not interrupted within the delay specified by HibernateDelaySec=, the system
will be woken using an RTC alarm and hibernated (the state is then stored on disk).
Settings in these files determine what strings will be written to /sys/power/disk and
/sys/power/state by systemd-sleep(8) when systemd(1) attempts to suspend or hibernate the
See this answer if you want to enable either
hybrid-sleep in your Ubuntu laptop.
Hope this helps.