Very new to training, abbreviation confusion

I'm clipping along happily in my sprint training program. The swimming portion had some abbreviations for strokes and techniques, but there was an explanation. I've now encountered a running one I do not understand.

I found the glossary link in this forum section, but I don't think "MS" in the context of "MS: 8-12 x 15" pick-ups, (strides) - about as fast as 5k pace" means "Multi-sport". Also, there are references to specific numbers of "Core" workouts, but I'm not sure what those entail.

I have to believe I'm missing one of the reading materials for this class. Without going into too much detail (because I realize training program support is a paid service), is there a general vocabulary manual I should purchase? Or, is there a portion of the site here I'm overlooking which might provide some detail? I have to believe without some background, I'm quickly going to drive you all crazy with a constant stream of the "what's this?!"

Thanks much for your time.