This is a basic feature found for example in the Polar software since forever.
Please let people give a name or write a description for each lap, instead of identifying them only by a progressive number. Progressive numbers work for runners who take an automatic lap every km/mile, but let others mark for example geographical places (a crossroad, the start and end of a climb) or training features (start and end of an interval or of a cycling group ride), or even, for those like me who take one of their Garmins to the gym, let me write down what exercise each lap corresponds to.
A couple of strictly related features which I'd like to see too, but not as important, and that can be found in for example Polar.
1) you can mark the lap not only with a text, but also an icon (a mountaintop, a crossroads, a U/turn, a start or end of interval, a drinking pause,...).
2) the lap texts are taken into account when searching for an exercise in your whole training history. This means if you mark with a lap a specific climb and later give the lap the climb name, you can just search for the climb name and find every single training when you did that climb.