Stack, the height of the bike; Reach, the length of the bike. Both are measured from center of bottom bracket to top of head tube.
Buying a bike and then getting it fitted is backwards... you're the constant and the bike should be the variable... The reason why you should always have a bike fit first is so you can purchase the bike with the geometry that is closest to your ideal. Body measurements is only a part of the bike fit... you also need core strength, flexibility, type of terrain you ride/race, length of your rides/races, current/future goals, current/previous injuries/issues, riding experience, etc. It's a lot of factors that will change your bike fit... for example, you wouldn't have the same fit for a 10k time trial as you would for a 118 mile Ironman bike leg...
WSD can be divided into three camps... manufacturers that design the bike ground up
(i.e. geometry change, carbon layup change, etc.
); standard geometry, but changes to equipment
(saddle, narrower handle bars, etc.
); and lastly, no change at all from standard bike, but just slap some pink colors on it and call it a WSD... They obviously not all the same... Plus, you may or may not need
(or fit
) a WSD bike... Some will, but many won't...
Forget any kind of measurements that an online site gives you... they can't take all the information needed into account.