What is the basic concept of goodwill??

Goodwill is not an tangible assets. Its depends on several factors,like brandname,relation with related authority but the most thing is difference between book value and face value of shares.

depends of veriety of circumstances or combination of it like location, honesty of the one running the business, the lack of competition

goodwill is the creditworthy of a company..
the going concern of a company depends on this goodwill..

Goodwill is an "intangible asset" on the balance sheet because it is not a physical asset like buildings or equipment.
Goodwill typically reflects the value of intangible assets such as a reputation of the business, strong brand name, good customer relations, good employee relations and any patents or trade mark.
Goodwill can often arise when one company is purchased by another company.
In an acquisition, the amount paid for the company over book value usually accounts for the target firm's intangible assets.