I think Skyscrapers are buildings that have more than 6 floors on them.

Also,

• As skyscrapers are taller than 6 floors they need special steel structure to hold their weight and this steel structure is usually called Skeleton
• They have lifts :) as people won't walk up to all these floors.
• Special arrangement is there to get the water supply to the top stories.

There are a lot of other technical issues such as wind pressure, load bearing capacity of the land also comes into picture as you go higher.