I have been playing the piano for 8 years and today I was reading the Katchaturian Toccata and I discovered a symbol, which can be seen below. I am mystified and searched for “Music symbols” but didn’t discover my symbol on Wikipedia, neither on YouTube nor anywhere else. In search for the symbol I came across this post on the site What does a straight line followed by a sharp point mean in a piano score when under notes?, but it did not list it. I searched for an hour without result, so here I am writing this question.
It is sixteenth notes played the same way as the first part of bar 118 in the left hand where it is written out. It will be a total of eight sixteenth notes because the symbol is written betweeen half notes, so the half notes indicates the total duration of the figure. Note that the symbol is two beams which is how you can see that it is sixteenth notes.
In the first part of bar 118 the figure is the duration of a quarter note for the first beat then a new figure on the second beat as opposed to the rest of the bar where there is the same figure for the duration of two beats.
Here is a page with definitions of this kind of abbreviations in music: https://en.wikipedia.org/wiki/Abbreviation_(music)
Here is an image from that page:
Here you can see an edition of Khachaturian's Toccata which clearly shows how to play it: Source: https://kupdf.net/download/aram-khachaturian-toccata-for-piano-pdfpdf_59683afedc0d60a159a88e76_pdf
And here is an image from that page with the relevant bars:
Tremolo. The notes before the lines are alternated as quickly as possible, for the two beats shown.
EDIT: it seems that the three notes will alternate with the second minim, although that isn't easy given the stretch between highest and lowest notes.