This is the 227th most frequent Russian word.
миллионов
"Миллионов" means "millions" (genitive plural form in Russian).
миллионов is used in the genitive plural case to agree with the numeral five, following Russian grammar rules for expressing quantities.
У этой книги тираж в пять миллионов экземпляров.
This book has a print run of five million copies.
миллионов is in the genitive plural case used after the phrase 'несколько миллионов' indicating a large but unspecified number.
Он подарил музею картину стоимостью в несколько миллионов.
He donated a painting worth several million to the museum.
миллионов is used in the genitive plural case in 'двух миллионов' to indicate the amount needed to reach a specific total.