A type of registration rights that confers on an investor the right to register his unregistered shares when either the invested company or other investors (shareholders) conduct a registration. That is to say, piggy-back rights allow investors to include securities in a registration statement that the company plans to file for a primary offering or some other purpose. So often, agreements of piggy-back registration rights include provisions excluding the the shares of piggy-back registration holders from an ongoing offering, especially in situations where underwriters finds out that market demand is not as large as originally expected and that adding piggy-back shares to the offering will have a negative effect on the share price.