It doesn’t have to be universal or comprehensive.
Frans Pennings 18, Professor of Labour Law and Social Security Law, Utrecht University, the Netherlands and Martin Seeleib-Kaiser, Professor of Comparative Public Policy, Institute of Political Science, Eberhard Karls University of Tübingen, Germany, “Social Security,” Routledge Handbook of the Welfare State, edited by Bent Greve, 2nd ed., Routledge, 06/28/2018, pp. 355–365 DOI.org (Crossref), doi:10.4324/9781315207049-32
The contingencies covered are traditionally the following: old age, survivors, disability, industrial accidents, unemployment, sickness, and maternity. In the definition it is attempted to characterise these schemes: they are linked with the physical situation of the person which means that he cannot work anymore (sickness, disability, old age) or a personal situation that has led to a loss of income (death of breadwinner). Unemployment is not related to the physical position, but is often the result of economic development.
This definition does not mean that there is also an obligation to give protection in all situations which fall within this definition. For instance, self-employed persons are hardly ever protected against loss of income due to economic developments. However, if a scheme meets the definition, it is considered part of social security.