Right of First Refusal - the shareholder must offer shares to the other shareholders before they can be sold to a third party.
Piggy Back Rights - If the majority shareholders choose to sell their shares, the minority shareholders can require that their shares are also sold.
Drag Along Rights - If the majority shareholders choose to sell their shares, they can force the minority shareholders to sell also.
A "shotgun clause" refers to a forced buyout. A shareholder offers to either sell its shares to the other shareholders, or to purchase their shares. The other shareholders make the decision as to which option they choose. The price must be the same for both options.