When editing a file with spell turned on, you may find vim highlighting
some of your content in red. This red highlighting indicates a misspelling.
Sure, these words technically aren't going to show up in something like the
Merriam-Webster dictionary, but as far as you are concerned, they are words.
They are part of your internal, shared language. The word admin is a great
example. Why not just tell vim once and for all that such words are valid.
You can do just that by moving your cursor over the misspelled word and
hitting zg. That will add it to the spellfile, a list of words, which
vim includes in its spell checking. This means vim will no longer highlight
that word red.