The Gross Yield is all of the distribution payments for the past year divided by the current unit price. This is shown as a percentage.
It shows the income stream you can expect based on an investment made today as separate from any capital growth (increase in share price) that might occur.
Please note: Yield is not guaranteed, although listed companies are reluctant to reduce or halt their dividends. See What’s the difference between a dividend and a distribution? for more.