Barbituates are a type of sedative - technically any drug derived from barbituric acid. They depress the central nervous system and, depending on their strength, can result in any effect from sedation to anesthetic.
Barbiturates were first developed in 1903 with the invention of barbitol. It was soon followed in 1912 with phenobarbitol. They were widely used in the first half of the 20th century as sleep aids. However, by the 1950s, it was noted that they resulted in dependence in users and had other harmful side effects. It was also very easy to overdose on barbiturates. As such, by the 1970s, their use became far more controlled. Their sedative use has largely been replaced by benzodiazepines, although barbiturates are still widely used for their anesthetic effect, particularly to "put people under" from a conscious state. They are also used as an anticonvulsant for certain types of seizure disorders.