Inline skates are a type of roller skate
yes, I remember rollerblading as a child.
inline skates typically have two to five wheels arranged in a single line.
Wow I didn't know they came with just 2 wheels! 
The in-line design allows for greater speed than roller skates
Wow, but how do you stop on inline skates?
Some, especially those for recreation, have a rubber "stop" or "brake" block attached to the rear 
On one skate or both?