Electroweak is the term for a generalized type of interaction between particles that encompasses both electromagnetic forces and the weak force. The electroweak force was conceived in the 1960s, defined such that different aspects of it show as the other two forces, yielding a single theory that explains both forces. The concept of the weak force was formulated earlier (1930s-1950s) as a force that could underly some radioactive phenomena, including beta decay.
The other two forces of nature besides electroweak are the strong force and gravity. Theories that extend electroweak to include the strong force are termed Grand Unified Theories or GUTs. Numerous candidate theories have been developed but none have been proved or widely accepted.