Yield is a measure of the fund's income distributions, as a percentage of the fund price. Morningstar calculates this figure by summing the income distributions over the trailing 12 months and dividing that by the sum of the last month's ending NAV plus any capital gains distributed over the 12-month period. Morningstar adds back capital gains to estimate what the fund's ending price would have been had it not distributed these gains; this makes the result more comparable to a stock yield because stocks do not distribute gains but rather simply increase in price.
Income distributions include interest from fixed-income securities, dividends from stocks, and realized gains from currency transactions.