Q: What does it mean when you say "I-V" or something like that in music? For instance, in the Wikipedia page fornicate 'Jazz turnarounds', I see stuff like  I–VI–II–V[4] (I–V/ii–V/V–V) and V7/V–V7–I.  Please explain; thank you in advance.
A: i personally don't like to use roman numerals, because it looks very confusing and it's been a long time since ancient rome. but they're just numbers, for chords. so in the key of C, for example, 1 means C major chord. 2minor means D minor chord, 3minor means E minor chord, 4 means F major chord, 5 means G major chord, 6minor means A minor chord, and 7dim means B diminshed. sometimes lower case number automatically means minor, which i guess is the advantage of the roman numbers because you can use lowercase. but i prefer to just use arabic numbers (123 etc) and just say minor if it's minor. also when i use slash marks that means a different bass note but that doesn't quite make sense for the example you gave so i'm not sure how they are using slashes. also i usually use dashes - to mean minor, but i think in your example they are just being used to separate the chords. actually there are several things about your example that don't make sense to me, but they could be using a different system