Basis is the value of an asset or liability according to numerous accounting and tax rules. Listed below are general descriptions of some of the various tax basis concepts.
S Corporation owners basis is stock value plus loans from the owner to the S corporation plus S Corporation profits minus S Corporation losses minus distributions to the owner. S corporation basis is important since an owner cannot take out more money than the owner has put in and the corporation earned without paying taxes. S Corporation owners cannot report a loss from an S corporation on their tax return if they have a negative basis. They do have to report profits even if there is negative basis.
Partnerships have two sets of basis, inside basis and outside basis. Inside basis is the basis that the partnership tax records compute for each partner. Inside tax basis is the initial investment  (cash or the value of some other asset) plus profits minus loses minus distributions. Outside basis is what the tax rules say a partners share has cost the partner. Outside basis is effected by what the tax rules say the investment in the partnership is worth. Outside basis begins with the basis of the partners original investment plus profits minus loses minus distributions.
 As an example, Johns father and Marys father each put $1,000 into a partnership. The partnership buys a piece of land for $2,000. There are never any profits or losses. Years later the land is worth $1,000.000. Johns father gives John his partnership interest. As a gift, John assumes his fathers basis of $1,000. Johns outside partnership basis is $1,000. Marys father dies and she inherits her fathers partnership interest. As an inheritance, Mary can step up the basis to fair market value. Marys outside partnership basis is $500,000. John and Mary put their partnership interests into a new partnership. Their inside basis in the new partnership is $500,000 each, half the value of the land. Johns outside basis is still $1,000 and Marys is $500,000.
Your Home The basis of your home is the original purchase price plus closing costs and points that have not been deducted plus permanent improvements. Improvements do not include maintenance items like painting. If you deferred a gain from a home sale prior to May 6, 1997, your basis is reduced by that deferred gain. If a depreciation deduction was taken for the rental or business use of your home, then your basis is reduced by the amount allowed to be deducted.
Inside Outside Basis has been the most popular search term creating traffic for this web site. The discussion in Partnerships above was not intended to be authoritative but rather a simple example for the need of professional advice.