What Causes Indentation With A Lump On The Calf Bone?

After shaving, I was putting lotion on my legs. I felt on my calf an indentation in the muscle...in the indentation there was a little lump that was firm, but also moved, if i moved my finger around it seemed to slide around in the "hole" i felt before. It's not visible if you're just looking at my legs, I haven't had any pain, this is also the first time I've felt it. Any idea what's going on here?