This is the 2514th most frequent Russian word.
прошлых
"Past" or "previous."
The word "прошлых" is used as an adjective to modify "выходных," indicating a temporal reference to a previous timeframe.
В этот музей я ходила в прошлых выходных.
I went to this museum last weekend.
Here, "прошлых" is used to describe "лет," referring to years that have already passed.
Посмотрите отчёты из прошлых лет.
Take a look at the reports from previous years.
In this sentence, "прошлых" is related to "времён" to signify times that are no longer current.