Stamps from the Federation of Malaya date from between 1900 and 1935. The Federation was comprised of four states that had to that point been issuing their own individual stamps: Negri Sembilan, Pahang, Perak, and Selangor.
When the Federation of Malaya was formed, the four states began using leftover stamps from Negri Sembilan, with overprints reading FEDERATED MALAY STATES. This lasted a very short time, however; soon, fully inscribed Federated Malay States stamps were designed and issued. It is both types that collectors, sellers, and buyers concentrate on these days, though the latter are more numerous and thus easily found.
When the Federation of Malaya was dissolved in 1935, each of the four states began issuing its own individual stamps again.
See also: South Vietnam rare stamps for philatelists and other buyers
Note: See also the Federation of Malaya, a collection of nine states that issued stamps during its existence 1948-1963.