What is a remainder?

"Remainders" are created in the language of the actual conveyance. They identify someone who will get rights to property after someone else's rights naturally end. In other words, they identify people who will get the remainder of the estate. For example, let's break apart this conveyance and figure out who owns what:

Oz conveys Blackacre "to Amy for 1 year, then to Bob for 2 years, then to Carl for life."

Amy has a present possessory interest in Blackacre.
Bob has a future interest in Blackacre. It is a remainder because it only comes into existence after Amy's interest naturally ends upon 1 year.
Carl has a future interest in Blackacre. It is a remainder because it only comes into existence after Amy's interest ends upon 1 year, and then after Bob's interest ends after 2 years.
Oz also has a future interest in Blackacre. His interest in a reversion, and it comes into existence after Carl's life estate terminates upon Carl's life. Why? Because land always needs an owner, and since the original conveyance didn't include someone after Carl's life estate, it must revert back to Oz and his heirs.

Note that Oz could make a second conveyance to Dan that conveys "all of my rights, title, and interest in Blackacre to Dan." What does Dan get? Dan gets all of Oz's rights, title, and interest in Blackacre, which is the reversion right (not a remainder).