How Power Grids Work

Power plants produce 3 phase. Your house may typically be wired to the grid using one of these phases. Transmission lines have 3 wires + ground. Terminal distribution power poles may have only 1 phase + ground.

https://www.science.smith.edu/~jcardell/Courses/EGR220/ElecPwr_HSW.html#:~:text=Most%20notably%2C%20it%20is%20produced%20in%20three%20phases.&text=The%20power%20plant%20produces%20three,ground%20common%20to%20all%20three.