What exactly do they mean when they say vaccine is “90% effective against symptomatic Covid-19 and 95% effective against severe disease”? A bit lost here… For

What exactly do they mean when they say vaccine is “90% effective against symptomatic Covid-19 and 95% effective against severe disease”? A bit lost here… For the first part, does it mean that 9/10 contacts with the virus, which should otherwise result in a symptomatic COVID, will not happen (or manifest through any symptoms), or it just means 9/10 vaccinated people don’t get symptomatic COVID (assuming everyone behaves the same). Second part is even trickier: does it mean that (a) 95/100 of all vaccinated will not contract a severe disease, (b) 95/100 of those that get exposed to a virus will not contract a severe disease, or (c) 95/100 infections will not result in a severe disease? I have a sense we also need a statistic covering asymptomatic infections, to get the full picture.