conservative definition of the word "decades": 7*7 years which is equivalent to 49 years at the minimum. (short sweet and concise with meaning...no changes, no alterations, always a true and perfect pattern)
liberal definition of the word "decades": 10 years is supposed to be equivalent to one decade, but we have determined that the number "0" in the number "10" has no definition, so we don't determine that there is such a thing as a decade. There may be a deck-of-spades which is an unusual deck of cards when teaching the meaning of "Random selection." So it means a "deck of spades."