A "simple knot" refers to a basic and easy type of knot that can be tied quickly. It is not complicated or intricate, but instead is straightforward and uncomplicated. Full definition
There is a natural numerical scale of complexity for knots, ranging from simple knots at the low energy end to more complicated ones higher up. (newscientist.com)
The leather straps are tightened and loosened by tying simple knots, and the top closes with a magnetic or snap closure. (treehugger.com)
It looks like a complicated macrame piece, but it's actually a series of simple knots and braids. (hgtv.com)