The interpretation really depends on what the cash flows represent. But one way to understand a monthly return of negative 27.41% would be to consider a stock portfolio that starts out worth $100,000 and after 12 months is worth $2,141 and after 18 months is worth a mere $313. I say 18 months (not 19) because with 19 data points, the first represents time 0, the second time 1, etc.
Or another way, if you simply add all 19 cash flow numbers you get $638,688. Now if you start with a stock portfolio worth $638,688 and experience a monthly return of negative 27.41% it would be worth $2,000 after 18 months. The difference between that $2,000 and zero (which is what the IRR converges on) is the fact that the cash flows are spread out over the 18 months and not all present at the start.
The result from the IRR formula is the periodic rate for the number of periods provided. (Initial investment, followed by periodic +/- cash flows) Since your formula included multiplication by 12, I inferred that these were monthly cash flows and so the result is a monthly rate of return (or loss as it turns out).
Accountants use this for proper comparison of investment alternatives. E.g., which is the better 3-year investment of $100,000 -- One that will return nothing for the first year and then return $1,000 a month after that (A), or one that returns $650 the first month and every month after that (B)?
(A) will pay out a total of $24,000 over three years, while (B) will pay out a total of $23,400 over three years. So is A better? No. If you anticipate that the value of the investment (in either case) will be $80,000 after three years, Investment A has a monthly IRR of .0917% while investment B has a monthly IRR of .1045%, so investment B is better.
Whew! I wasn't planning on being so long-winded. Well, maybe it's because I'm starting on an 8-day vacation tomorow morning. If you have a reply, I'll see it next week.