A more thorough explanation:

INSTITUTIONES

In Roman law, institutiones refer to elementary works of law or institutes. It can also refer to:

1. A legal treatise or commentary, such as Coke's Institutes in four volumes.
2. An elementary treatise on Roman law in four books, which is one of the four component parts of the Corpus Juris Civilis. This treatise is also known as Institutes of Justinian or Justinian's Institutes.
3. An elementary treatise written by the Roman jurist Gaius, which served as a foundation for the Institutes of Justinian. This treatise is also known as Institutes of Gaius.
4. A paraphrase of Justinian's Institutes written in Greek by Theophilus, a law professor at Constantinople who helped prepare the Institutes of Justinian. This work is also known as Paraphrase of Theophilus or Institutes of Theophilus.
5. In civil law, a person named in a will as heir, but under directions to pass the estate on to some other specified person (called the substitute). This person is also known as a substitute.
6. An organization devoted to the study and improvement of the law, such as the American Law Institute.

• Coke's Institutes in four volumes is a legal treatise that provides commentary on English law.
• Justinian's Institutes is an elementary treatise on Roman law that is one of the four component parts of the Corpus Juris Civilis.
• Gaius' Institutes is an elementary treatise on Roman law that served as a foundation for Justinian's Institutes.
• The Institutes of Theophilus is a paraphrase of Justinian's Institutes written in Greek by Theophilus.
• A substitute named in a will as heir, but under directions to pass the estate on to some other specified person, is an example of an institutus.
• The American Law Institute is an organization devoted to the study and improvement of the law.

Institutiones refer to elementary works of law or institutes in Roman law. The examples illustrate the different meanings of institutiones, such as legal treatises, elementary treatises on Roman law, and organizations devoted to the study and improvement of the law. The examples also show the different names used for institutiones, such as Institutes of Justinian, Institutes of Gaius, and Institutes of Theophilus.