Orthography

Etymology

From Greek orthos ("straight, correct") + graphein ("to write"), literally "correct writing." The orthos element is the same one in "orthodox" (correct belief) and "orthopedic" (straightening). Orthography names the socially agreed standard for putting a language on the page — a standard that can differ across countries speaking the same tongue.

noun · /or-THOG-ruh-fee/
The conventional spelling system of a language — its accepted rules for writing words correctly.
What it names
The agreed-upon rules of the written page, which is why "colour" and "color" are two orthographies for one word rather than a mistake.
Example
English orthography is notoriously irregular: "though," "through," and "tough" share letters but not sounds.
Related idea
Orthography concerns how words are correctly spelled; a phoneme concerns the sounds themselves. English pain comes largely from the loose fit between the two.