The par value of a share is the value stated in the corporate charter below which shares of that class cannot be sold upon initial offering; the issuing company promises not to issue further shares below par value, so investors can be confident that no one else will receive a more favorable issue price.
For example, Delaware permits the issue of stock either with or without a par value, but by choosing to assign a par value, a corporation may significantly reduce its franchise tax liability.
Instead of par value, some U.S. states allow no-par stocks to have a stated value, set by the board of directors of the corporation, which serves the same purpose as par value in setting the minimum legal capital that the corporation must have after paying any dividends or buying back its stock.
The term "at par" is also used when two currencies are exchanged at equal value (for instance, in 1964, Trinidad and Tobago switched from the British West Indies dollar to the new Trinidad and Tobago dollar, and that switch was "at par", meaning that the Central Bank of Trinidad and Tobago replaced each old dollar with a new one).
Par value also refers to the official gold content of a currency.