Lxqt-panel represents the taskbar of LXQt.

The elements available in lxqt-panel are called "plugin" technically.
This applies e. g. to the source code where they reside in directories
./plugin-<plugin> like plugin-mainmenu.
In contrast to this they are called "widgets" by the configuration GUI
so far.
Also, a more descriptive term is used to refer to distinct plugins within
the GUI. E. g. the aforementioned plugin-mainmenu is called
"Application menu" that way.