Capital assets are defined in section 1221 of Internal Revenue Code (IRC) to mean a property of any kind whether or not connected with his trade or business. However , following kinds of property is not considered “capital asset” :
If property is a stock in trade or primarily for sale to customers in the ordinary course of his trade or business;
If the property, used in his trade or business, gets allowance for depreciation provided in section 167, or real property used in his trade or business;
a patent, invention, model or design (whether or not patented), a secret formula or process, a copyright, a literary, musical, or artistic composition, a letter or memorandum, or similar property developed by a taxpayer or n the case of a letter, memorandum, or similar property, a taxpayer for whom such property was prepared or produced
There are other finer points and exclusion in the definition of capital asset.
Whenever you sale or exchange or transfer any property that falls under the definition of “capital asset”, the gain will be charged as “capital gains ” and if such a property is held for more than 12 months before sale/transfer , the gain will be classified as “Long Term Capital Gains” which is taxed at much lower tax rates. You can estimate capital gains by using capital gains calculator.