What does "jillion" mean?

An unspecified large number (of).

What is a synonym for "jillion"?

Common synonyms include: gazillion, zillion, a billion, a crore, a lakh, a million.

/ˈd͡ʒɪljən/ noun, slang

noun, slang ·Moderate ·High school level

Noun

1
An unspecified large number (of). excessive, slang
"I know this has been asked a jillion times, but news server displays only one days^([sic]) worth of posts.."
2
a very large indefinite number (usually hyperbole) wordnet

"I know this has been asked a jillion times, but news server displays only one days^([sic]) worth of posts.."

See -illion.