A definition of the electroweak force is given by ref. 1 as:
The electroweak force is a force proposed by physicists Sheldon Glashow, Abdus Salam, and Steven Weinberg which unifies the electromagnetic and the weak force under conditions of extreme temperature prevalent much earlier in the history of the universe. The symmetry corresponding to this unification has since been "broken," with the ensuing expansion and drop in temperature of the universe yielding two of the four fundamental forces known today. When the electroweak unification energy (around 100 GeV) is achieved locally, for example in particle accelerators, the distinction between the electromagnetic force and the weak force disappears.
Hence this force is only relevant in extreme environments like early in the birth of the universe or in high energy physics experiments. A simple description is given in Ref. 2 and 3. the Nobel Prize was awarded to Glashow, Salam, and Weinberg in 1979 for their working leading to the Electroweak Theory.
ref. 1. http://www.daviddarling.info/encyclopedia/E/electroweak_force.html
ref. 2. http://hyperphysics.phy-astr.gsu.edu/hbase/Forces/unify.html
ref. 3. https://en.wikipedia.org/wiki/Electroweak_interaction