Similar to touch potential is step potential: the voltage difference between the two feet of a person standing near an energized, grounded object.
When an energized object, such as a downed power line contacts the ground, electric current will flow into the ground. At high enough voltages, the electricity spreads out in concentric circles from the point of contact. This is referred to as a voltage gradient because the voltage is highest at the point of contact and decreases with distance outward.
If you step across a voltage gradient, you could be electrocuted. One foot will have a higher voltage than the other, and electricity will use your legs as a path to equalize it. Similarly, step potential can affect two people carrying a long conductive object such as a metal ladder. Electricity can flow up one person’s legs, through the object, and down the other person’s legs, causing serious injury to both.