What are these two marking across the stem of the notes?

Question

I have come across some markings on the stem of the notes that I have not seen before. I have underlined them in the image below:

Strings section (violins, viola, cello and double bass)

My initial research at first glance suggested ‘Tremolo’; these markings have three dashed lines.

The Wikipedia answer below has confused me. What does Frequency mean here? What impact does this have on how the note is played?

Wikipedia: Instruments and their symbols

Answer 1

The number of slashes correspond to the number of beams that the notes would have if written out. Your example has two slashes, so this is shorthand for sixteenth notes filling the duration of a quarter note, which would mean four of them. Also note the four dots above the notes, this is to help indicate that exactly four notes are desired as opposed to playing as many notes as possible as fast as possible, as the Wikipedia article says.