Systemd, also shitstemd, is a horribly disastrous [bloated](bloat.md), [anti-Unix](unix_philosophy.md), "[FOSS](foss.md)" "software suite" used for initialization of an [operating system](os.md) and handling services like logging in or managing network connections. It is a so called [PID 1](pid1.md) process, or an [init system](init_system.md). Systemd has been highly criticised by the proponents of [suckless](suckless.md) and [LRS](lrs.md) and even normies for its enormous amount of bloat, ugliness, anti-Unix-philosophy design, [feature creep](feature_creep.md), security vulnerabilities and other stuff. Unfortunately it is being adopted by many [GNU](gnu.md)/[Linux](linux.md) distributions including [Arch Linux](arch.md) and [Debian](debian.md). Some distros such as [Devuan](devuan.md) just said no to this shit and forked to a non-systemd version.
For more detailed bashing of systemd see e.g. https://nosystemd.org/. The site sums up systemd with a fitting quote: *"If this is the solution, I want my problem back*". Another sum up by [suckless](suckless.md): http://suckless.org/sucks/systemd/. There is also e.g. https://sysdfree.wordpress.com/.
