What's a 30-day yield on a mutual fund?

I see that some of mutual funds that feature 3~5% 30-day yield. Does that really mean they will yield 3~5% in 30 days? So, if I put in a million dollars in a mutual fund like that, what do I get?

No, it does not mean they will provide that yield in the next 30 days.

The SEC 30 day yeild is a statistic provided for mutual funds that generate income in the form of interest or dividends from debt securities.

If my memory serves me correct, this is an annualized figure based on the income from the previous 30 day period. Like other statistics on investments, this is a look at the past and does not predict or guarantee future performance. You would still want to look at the longer term return figures such as the 1, 3, and 5 year average annual returns.

No, when people say yield, they mean APY (annual percentage yield).
It's usually annual unless they specify.
5% 30 day yield means you will get 5% APY.
The actual yield you will get if rates don't change is to divide 5% into 12 months.
ie .05/12=.004167 which is .4167 of 1%.
If you have 1000 invested, you will get $4.167 in interest.
That's the basic, if you want the exact number you need a financial calculator.
30 day yield for mutual fund is like buying a month bond.
Mutual fund bonds can go up and down in price, therefore the yield changes.
If the Fed increase interest rate, your bond fund will drop in price and increase in yield.
Overall, you will lose money.
It's vice versa.
So, if you want something safe, put it in money market fund.
Nowadays, you can get a high savings rate directly from the bank.
ie. HSBC Direct 5.05% (6% promo)
Check them out at bankrate.com.
I prefer HSBC because it's a brand name and I can link it to my HSBC bank's checking account.
It's faster to get cash or invest your savings.