It depends what discipline one is coming from and also what political lens one views that question through. I would say (as an anthropologist activist) that a livelihood is sustainable when it supports the health and wellbeing of the person and is resilient enough to deal with changes and stresses. A sustainable livelihood would also give an equal or greater return of the labour (and other forms of work) invested in the livelihood in ways that are meaningful to the person. A sustainable livelihood protects the assets used in that livelihood, and is able to restore the natural resource base considering the planetary boundaries and also limitations of local resources.
I would simply say, A livelihood doesn't harm our natural ordination and make sure restoration of nature and extracting natural goods without interrupting its heavenly communication.
sustainable livelihood means to secure the way people make a living. The sources of livelihoods are e.g. work related incomes (salaries, wages, income from own company), incomes from social connectedness (e.g. remittances), state transfers (e.g. social welfare), pensions and other benefits people have contributed to...... Over the past 30 years a number of appraoches have been published of how to secure livelihoods. Central to these appraoches are livelihood capitals (usually natural, physical, financial, human and social capital). These capitals can be seen as assets people use to secure / make sustainable (lasting) their livelihoods, especially against shocks, adverse trends and seasonabilty......