When my 8 yr old daughter did this phrase on Duolingo, I had a flash memory of my Magyar parents making me "Kis katonak"...Magyar bacon (szalona) on bread, cut into 2cm cubes, little bread & bacon stacks, they called "Kis katonak". Did anyone else ever hear of this, or was it just something my WWII parents had been made by their WWI parents (my grandparents)?
We had the same in our family, except we called it "katona" only. Basically any bite-sized sandwich-like contraption could be called "katona". We usually used sausage slices or other processed meat or even liver pate. My parents were born after WWII. I did not hear it recently, not sure if it's still common.
Reminds me of "eggy soldiers", where the soldiers are long, thin, pieces of toast for dipping. Example: https://www.deliciousmagazine.co.uk/recipes/boiled-egg-with-soldiers/
Hm. How weird. In that case it must be a word that is part of an accepted answer in some sentence. I haven't come across it, so I don't know exactly where.
It probably stands for "szerkezet elején" which means roughly "at the front of the structure". It might be a grammatical note for some word order rule.
It's probably from a hint somewhere -- likely from the "English for Hungarian speakers" course if that exists, where some English word is glossed with a Hungarian word and that note "szerk.elején" in parentheses -- something intended to be seen only by a Hungarian leaner of English peeking at the word hints.
Unfortunately, the word tiles for tapping exercises seem to be generated at least partly from the hints, including such explanatory additions that are not necessarily real words.
The German course has the masculine and feminine symbols (circle with arrow / circle with cross) crop up in tapping tests occasionally because those symbols are used in hints to show that e.g. Lehrerin means specifically a female teacher.