손절 후 30일 이후에 같은 주식을 매입하는건 와시세일에 안걸리는 거라고 알고 있었는데 피델리티 웹싸이트 명시되어 있는 61-day window 는 또 뭔지 혹시 아시나요?

What is the wash-sale rule?
When you sell an investment that has lost money in a taxable account, you can get a tax benefit. The wash-sale rule keeps investors from selling at a loss, buying the same (or "substantially identical") investment back within a 61-day window, and claiming the tax benefit. It applies to most of the investments you could hold in a typical brokerage account or IRA, including stocks, bonds, mutual funds, exchange-traded funds (ETFs), and options.

More specifically, the wash-sale rule states that the tax loss will be disallowed if you buy the same security, a contract or option to buy the security, or a "substantially identical" security, within 30 days before or after the date you sold the loss-generating investment (it's a 61-day window).