What is rucking exactly

Okey i got it. Rucking is kinda hybrid exercise which combines cardio and resistace training you can overload weight speed time parkour etc. But what should one expect from it? I do resistance training full body 2times week for a few month. I am swimming regularly for a year and half.

I have a good cardio capasity when it comes to swimming but I have a bad posture (neck and lower back hernias) and below avarage ör maybe avarage strenght. For a year ago i lost 15-20 kgs witout resistance training that made me less strong i guess

So what is rucking exactly. İ am planning to do it once per week (2gym and 2 swimming) which lover body exercises should i add to gym routine (lower legs and butt are covered with rucking i guess ör is it?) adding leg curl and extension is allright?