Yes, that's a split. Usually caused by uneven watering. Temperature extremes can do it, too. Tomatoes like to be kept evenly moist, so if the soil gets dry and then it rains heavily, they plump up too quickly and split. Or if you keep letting the plants dry too much between waterings.
They are still perfectly edible. Just cut off the split part. However, the splits also make the tomato vulnerable to insects and nasties like fungus and bacteria, which can eventually damage or destroy it. I had a lot of trouble with splitting earlier this year because I grew my tomatoes in pots and didn't regulate the watering properly when the weather heated up. I just kept an eye on them and as long as it didn't look like there was anything amiss, I left them on the vine. I picked a couple early (red, but not quite fully ripe) because the splits were getting big and I wasn't willing to take the chance of losing them. Your tomato is still pretty green and that split isn't very big, so leave it. Just keep watch for changes in its appearance.
