Dreams possess the capacity to incorporate memories from your daily life, such as a person you've met recently or someone you've known your whole life, but the meaning and use of this phenomenon is unknown. Most dreams just piece together bits of memories.
The science of dreaming, called oneirology, and the technology used to study it have come a long way since Sigmund Freud's famous treatises on dreaming were published. A dream can be roughly defined as any sensation, thought, emotion or image experienced during sleep. Beyond this definition, the content and purpose of dreams remains under dispute. Numerous theories exist, and most have evidence to back up their claims.