Every field has it’s own set of vocabulary that to an outsider may make zero sense.  Designers use terms like orphan and widow to identify issues that can interfere with legibility. What is important is not learning the design jargon, but becoming familiar with common typographic mistakes so that they can be identified and avoided in your own writing and layouts.

A widow is a paragraph-ending line that falls at the beginning of the following column or page. Like this:

An orphan is a paragraph-opening line that appears by itself at the bottom of a page or column. The term is also commonly used to refer to a word or short line that falls alone at the end of a paragraph or line. Like this:

A river is a line of negative space that runs throughout a paragraph. It is frequently caused by fully justified text, creating too much space between words within a line of text. Like this:

Widows, orphans, and rivers are problematic because they create awkward edges and breaks in the text, interrupting the reader’s eye and leading to legibility and comprehension issues.

If you’re interested in learning more about typography The Elements of Typographic Style by Robert Bringhurst (Hartley and Marks Publishers, 3rd ed. 2004) is a great resource!  What are some terms you use that may seem like gobbledygook to an outsider?