Can somebody help me determine what this music symbol means?

I was reading an advanced piece of piano music and I saw a symbol that is unknown to me. It's kinda like a gliss (that thin diagonal line that goes from one note to the other), except that the line is thicker (bold) and there are three of them. Basically, it's like three bold & diagonal lines that go from a low C to a higher C. Please help me? Thank you!