The definition of a twin bed is a small piece of furniture with a mattress designed for a single person to sleep upon.
An example of a twin bed is a dorm bed in college that has room for only one person.
either of a pair of single beds
A bed intended to fit one individual, usually measuring about 39 by 75 inches (99 by 190 centimeters), and traditionally one of a set of two.
(plural twin beds)
- Either of a pair of matching single beds.