Such a group may be a group of individuals (organised or not), an institution, organisation or company. Some examples may be the army, an industrial company that manufactures or develops the artefact, or consumers/users of the artefact. However, to identify relevant social groups as only being producers and consumers of a technology is reductive; there are numerous other groups in addition to these two.
For Bijker, a social group is relevant when the meaning of the artefact is the same for all members of that group.
Bijker uses his study of the history of the bicycle to give the example of cyclists, as users of this technology. However, within this group there are also sub-groups; in this instance, women cyclists, for whom the bicycle came to mean emancipation and a vehicle (excuse the pun) to take them into the twentieth century.
One artefact will have several relevant social groups and each group will have greatly differing interpretations of that same artefact. A nuclear reactor serves as an example. Note the varying interpretations of these social groups:
Union bosses - a safe working environment compared to, say, a building site or dockside.
Local residents - dangers of radioactivity and attendant cancers, but also employment opportunities.
International relations experts - the presence of a nuclear reactor causes unrest in the international community (and nuclear proliferation) especially when in the hands of someone we're not too friendly with!
Conclusion - "interpretative flexibility"
Trevor Pinch, Wiebe Bijker. "The Social Construction of Facts and Artefacts: Or How the Sociology of Science and the Sociology of Technology Might Benefit Each Other."