North Dakota must contain the word "company", "corporation", "incorporated", "limited", or an abbreviation of one or more of these words; may not contain the words "limited liability company", "limited partnership", "limited liability partnership", "limited liability limited partnership", or any abbreviation of these words. North Dakota century Code 10-19.1-13
PLLC, Professional Limited Liability Company: some states do not allow certain professionals to form an LLC that would limit the liability that results from the services professionals provide such as doctors, medical care; lawyers, legal advice; and accountants, accounting services; architects, architectural services; when the company formed offers the services of the professionals. Instead those states allow a PLLC or in the LLC statutes, the liability limitation only applies to the business side, such as creditors of the company, as opposed to the client/customer service side, the level of medical care, legal services, or accounting provided to clients. This is meant to maintain the higher ethical standards that these professionals have committed themselves to by becoming licensed in their profession and to prevent them from being immune (or at least limit their immunity) to malpractice suits.
LLC, LC, Ltd. Co., Limited Liability Company: a form of business whose owners enjoy limited liability, but which is not a corporation. Allowable abbreviations vary by state. Note that in some states Ltd. by itself is not a valid abbreviation for an LLC, because in some states (e.g. Texas), it may denote a corporation instead. See also Series LLC. For U.S. federal tax purposes, in general, an LLC with two or more members is treated as a partnership, and an LLC with one member is treated as a sole proprietorship.
Limited liability companies are easy to maintain while remaining extremely flexible, so it's not surprising that it is a popular choice among businesses of all different shapes and sizes. Often, owners of an LLC are self employed or run smaller businesses, where the simplicity of pass through taxation and a lack of annual requirements makes a lot of sense. Since the profits and losses are reported directly on the owners personal tax returns, filing taxes is much easier.
Unltd or Ultd (Unlimited/無限公司): similar to a limited liability company (Ltd) but whose members or shareholders do not benefit from limited liability should the company ever go into formal liquidation. It is not a requirement under company law to add or state the word or designation Unlimited (無限公司) or its abbreviations (Unltd or Ultd) at the ending of its legal company name, and most unlimited companies do not.