Correct spelling, explanation: referring is a present participle form of the verb to refer. Referring has its origin in the Latin form referre, which meant to carry back. It actually joined two words – re meaning back and ferre meaning bring. Referring also existed in Old French, in the form referer. Finally, in the Middle Ages, referring entered English.

Definition of referring:
1. verb (Present Participle form) – to mention someone or something only in a few words,
In her autobiography, she’s only referring to her second husband, which was a surprise to everyone.
2. verb (Present Participle form) – relating to someone or mentioning someone,
Referring to John in the context of that situation was unfair as he had nothing to do with it.

Expressions with referring:
A few commonly used expressions with referring include: briefly referring, cross-referring, and jokingly referring.
He is briefly referring to those numbers in the report, but in my opinion, it deserves much more attention.
Cross-referring makes an article more reliable so the technique is often used by journalists.
He is jokingly referring to her ex-wife in the book, which will make her go mad.

Incorrect spelling, explanation: one of the most common spelling mistakes in referring is to write it as refering – with a single -r letter before the -ing ending. It is true that the base form of referring is refer and it features a single -r letter, but when we add the ending, we need to double the -r letter so the only correct form is referring.