philosophical
पर्वन् parva
parvan
root √pṛ — to fill — hence "knot, joint, section"
A "knot" or jointed section of a long text. The Mahābhārata has eighteen major parvas, subdivided into sub-parvas.
A parva is a knot or articulation — like the joint of a bamboo. The metaphor implies that a long composition is structured by its joints, not by chapters in the modern sense. The Mahābhārata’s eighteen parvas are its primary articulation; each parva contains sub-parvas, each sub-parva contains adhyāyas, each adhyāya contains verses.
The number eighteen is significant: eighteen days of war, eighteen books, eighteen chapters in the Gītā, eighteen akṣauhiṇī armies destroyed. The text is fond of the structure.
The standard Critical Edition divides the eighteen parvas into about a hundred sub-parvas; sub-parva names are often more evocative than parva names (the Anukramaṇikā-parva, the “table of contents” sub-parva, sits inside the larger Ādi-parva).