Um, it'd probably be easiest if you went to mathword or something to look it up. It's basically a log but base e (no duh). ln = log base e. As you probably saw from doing exponentials, e is a special number in that d/dx(e^x) = e^x and Se^x = e^x+c
lnx is equally as elegant. d/dx(lnx) = 1/x and so S(1/x) = lnx+c. The integral of lnx is not dealt with in the 3u course, but if you need to find a definate integral of it you can just find the corrosponding area under e^x.