Microsoft Style Guide confirms system tray is wrong, but search shows it’s used a lot anyway…
Don’t use. Use notification area instead.
On Linux, some people call them indicators. Here’s history from a possible future indicator source.
The panel indicator area was introduced in an early version of GNOME somewhat based on the Microsoft Windows '95 design, as an area dedicated to notifications. It is often called the systray or the notification area.
Here’s a Linux one, which is similar to Windows’. Icon has a menu, and changes color and shape.
Make System Tray icon a little bit more informative is a request to do more with this, but more basic is disappearance of the currently used indicator software, slowly maybe replaced by Ayatana Indicators.
EDIT:
As this change progresses, even installing gets tough:
Duplicati fails to install at Centos 8 #3950
libappindicator is not part of OpenSUSE - why is it needed? #3804