There is widespread agreement in the literature that currently there is no generally accepted definition for the special form of volunteering, namely informal volunteering. Consequently, informal volunteering is usually distinguished from formal volunteering by its most striking feature: the lack of formality. Therefore, the aim of this study is to open up new perspectives for the interpretation of informal volunteering, – based on the results of analyses of informal volunteering, – that go beyond simplified interpretations that merely emphasise the lack of formality. To this end, we interpret informal volunteering not only in relation to formal volunteering, but also in relation to (reciprocal) assistance – as interpreted by Max Weber and Karl Polányi. This allows us to understand the differences and similarities between the main forms of voluntary supports. In the comparative analysis, we identified six categories of analytical criteria – the historical context as well as the socio-political, organisational sociological, social-psychological and psychological criteria for defining volunteer service – and additionally included eleven analytical perspectives. On this basis, two fundamental characteristics were identified that clearly distinguish reciprocal assistance, informal, and formal volunteering: the range of stakeholders and the structural characteristics. At the same time, more common features than unique differences between the main forms of support were identified. These included: the nature of unpaid work, the method of access, the duration of support, and the motivational background. In addition, reciprocal assistance and informal volunteering were grouped together based on the examination of the following criteria: lack of formality, the general characteristics of the form of participation, and the nature of prosocial behaviour. Finally, we were able to identify the commonalities between formal and informal volunteering based on non-reciprocal assistance, the criterion of "free will", the type of participation, and the similarity of motivations, which also distinguish them from reciprocal assistance. This study concludes that informal volunteering should be viewed as a transitional form of support between the reciprocal assistance and the formal volunteering, on the one hand, and as resource for recruitment, on the other. Furthermore, informal volunteering is the form in which the need for residual support for the household/family level is first addressed and where community activities gain importance.

Keywords: reciprocal assistance, informal volunteering, formal volunteering, support, organizational form, volunteer definition, form of participation, motivations