Window dressing
At the end of each quarter, mutual funds try to dress up their portfolios by buying the stocks that have had the best performance during that quarter. They do this to mislead potential investors into thinking that the fund's managers are great stock pickers. For example, if semiconductor stocks did well during the quarter, funds may load up on them during the last week of the quarter so their "holdings" list will give the impression that they have a clue what they're doing. It's completely superficial, and that's why it's called "window dressing."