Notation Question

Hi guys,

Just a quick question: What does this mean (the dark black lines between the notes)?

Thanks!

I do believe that indicates a tremolo.

A tremolo between two usually distant notes. 

I think they are more often than not seconds and thirds, but they don't have to be as long as it's idiomatic to the instrument it's wiritten for. For violin it must be reached by two fingers. On a piano it can be as wide as two hands, several octaves apart. And the rhythm is  denoted by the number of black lines. one for 8th notes, two for sixteenth, three for 32nd notes, etc. Tremoloes are just a kind of shorthand.