“Partnership” includes a syndicate, group, pool, joint venture, or other unincorporated organization, through or by means of which any business, financial operation, or venture is carried on, and which is not, within the meaning of this part, a trust or estate or a corporation.

“Partner” includes a member in such a syndicate, group, pool, joint venture, or organization.

A person shall be recognized as a partner for income purposes if he owns a capital interest in a partnership in which capital is a material income-producing factor, whether or not

such interest was derived by purchase or gift from any other person.