Being an essential and permanent part of something.
Being an included feature that normally comes as an extra.
Constructed as a non-detachable part of a larger structure.
Anything (such as a piece of furniture, or a software feature) that is built in, not added as an extra.
Being a type of company, a legal entity where the ownership has been arranged into shares. A shareholder has no responsibilities to the company and the potential losses of the shareholder are limited to the value of the stock turning to zero in the case of a bankruptcy.