Subsidiarity is understood as an institutional and social process orientated to some basic principles that connect vertical and horizontal directions:

• the capacity of individuals and/or smaller social groups to take care of themselves should not be hampered;
• higher or bigger organisations can intervene only when and where the lower or smaller scales do not have this capability; this is the "vertical" direction of subsidiarity that favours devolution of policy making to lower levels and smaller dimensions
• all levels of society should improve the relationships between the private and public sides; this is the “horizontal” direction of subsidiarity that gives to individuals and their communities scope and responsibility to organise and manage public functions by themselves;
• the subsidiary role of higher or bigger organisations must be temporary in nature; their basic commitment must be to allow individuals and/or minority groups to provide for themselves, to attend to their needs; that is to develop self-management, self-administration and self-governance, by means of empowerment and capacity-building;
• organisational systems should provide and assure flexibility and adaptability, in both vertical and horizontal directions, in order to give cohesion between their members; this means adopting a style of “multi-level governance”, where vertical relationships between higher and lower levels, larger and smaller dimensions, are conceived and managed in a horizontal way, respecting authoritative roles according to a value added scale.

Subsidiarity saw its origin from military language. Subsidiarity comes from the Latin concept of subsidium, which indicated the reserves (the supporting troops). The support (subsidium) to the front lines is temporary. If reserves substitute definitely the front lines, it means that the risk to lose the battle is high and then the security of a country is endangered.
One of the well known definitions of subsidiarity comes from the catholic social doctrine (Pope Pius XI “Quadrigesimo Anno” encyclical - 1931). Pius XI used specifically the terms “subsidium afferre” and “subsidiarii officii” to characterise the temporary role of support that a larger and higher society (or body) should have to not destroy and absorb those which are smaller and lower.
However subsidiarity-related principles are present in both the ancient and recent past, in texts related to the relationships between individuals and their social organisations. Aristotle, Thomas Aquinas, Locke, Tocqueville, Proudhon, Jellinek and others discussed and wrote on these topics.
Subsidiarity seems to be a word conceived by the Western civilisations, but its basic principles are present in other philosophies and mysticism (e.g., Buddhism, Hinduism, Gandhism): self-government, self-improvement, individual responsibility for oneself and for society, compassion and individual commitment, societal and individual action and change, etc.