[mch82]

Ridesharing is when a group of people rent a van through a ridesharing program and one of those people drives it. The driver is kind of like a school bus driver.

Carpooling is when 2+ drivers ride together in a car one of them owns instead of everyone driving separately.

[kelnos]

I've never heard of your ridesharing example before. When people do that I still hear it called carpooling, just perhaps, "we rent a van and carpool".

[gowld]

It's called vanpooling, often, obviously.