Whether you capitalize "mom" depends on how you are using the word. Is it a nickname, a common noun, or a term of endearment?
When “mom” is descriptive, it's lowercase. When it's used in place of a name, like a nickname, it's capitalized.
Scribes writing with the early Roman alphabet didn’t have to choose between uppercase and lowercase letters because there were no lowercase letters—all the letters were what we think of today as capitals. Lowercase letters came much later, as did the names “uppercase” and “lowercase.”
Uppercase and Lowercase
In 1382, the Wycliffe Bible was the first written reference to mention “capital” letters, according to the Oxford English Dictionary. The terms “uppercase” and “lowercase” came later and reflected the way compositors arranged the boxes that held the individual letters used in printing. The larger letters were literally stored in an upper case, and the smaller letters were stored in a lower case (along with the type for punctuation and spaces).
Printers Helped Determine Capitalization Rules
In addition to giving us the names “uppercase” and “lowercase,” printers also played a role in standardizing English capitalization. When compositors were turning handwritten manuscripts into printed documents, they often faced indecipherable handwriting, so they simply made their own decisions about which words should be capitalized. These early printers started the practice of capitalizing all nouns in English—a trend that has since fallen away but that was prominent in the 18th century. In fact, the US Constitution, written in 1787, not only codifies the birth of our nation but also serves as an easily accessible example of capitalized common nouns.