Equity multiple measures how many times you get your invested cash back over the life of a deal. You divide the total cash the property returns to you, meaning every distribution plus the net proceeds when you sell, by the total cash you put in. An investment that returns $200,000 on $100,000 invested has a 2.0x equity multiple: you doubled your money.
Unlike internal rate of return, the equity multiple ignores timing, so it does not care whether you doubled your money in three years or fifteen. That is exactly why the two are read together: IRR tells you how fast, the equity multiple tells you how much. A high IRR on a quick flip can still produce a small multiple, while a modest IRR held for many years can multiply your capital several times over.