The phrase "bicycle built for two" refers to a tandem bicycle that can accommodate two riders. Some synonyms for this phrase include "tandem bike," "double bike," "duo cycle," and "two-seater bike." These terms all describe a bicycle designed to carry more than one rider, with one person sitting behind the other. Tandem bikes are a popular choice for couples or friends who want to ride together and enjoy the outdoors. They can also be used for cycling tours, races, and other group activities. Whatever you call it, the "bicycle built for two" is a fun and unique way to enjoy cycling with someone else.