I just started playing the game and reading manual, watching tutorials etc but somehow I couldn't find the answer of my question. It should be very easy thing but I really couldn't manage to find it anywhere xD What is the liquid icon below the army readiness icon when we are viewing ground ...

I just started playing the game and reading manual, watching tutorials etc but somehow I couldn't find the answer of my question. It should be very easy thing but I really couldn't manage to find it anywhere xD What is the liquid icon below the army readiness icon when we are viewing ground units ...