Almost every NGO has a Corpus Fund and a General Fund. What do these donation options mean?

To be sustainable, NGOs need to build up a strong organisation. Given the erratic nature of funding, developing a corpus/general fund is one way that NGOs can do this. When you donate to the corpus/general fund, this helps NGOs to design long-term programmes without worrying about programme support from aid agencies, and to meet some organisational costs that no one else is willing to bear.

Essentially, corpus/general fund donations are not earmarked for a specific purpose, and the NGO is thus free to use them as required [e.g., to meet fundraising costs, or to conduct a training programme to upgrade skills of its own staff, or to launch a new project etc.]

Funds in the general fund can be used at any time, whereas money in a corpus can normally not be touched - the organisation is supposed to use only the interest that accrues from investments made out of corpus donations, without touching the principal itself.