Real Dictionary

quarterly
adjective: A quarterly event happens four times a year, at intervals of three months.

quarterly in American English
a publication issued every three months
occurring or appearing at regular intervals four times a year
once every quarter of the year
adjective: occurring, done, paid, issued, etc., at the end of every quarter of a year
adverb: by quarters; once each quarter of a year
noun: a periodical issued every three months

quarterly in British English
adjective: occurring, done, paid, etc, at intervals of three months
adverb: once every three months
noun: a periodical issued every three months