Surface Tension ($T$ or $S$) is the tendency of liquid surfaces to shrink into the minimum surface area possible.

1. Force Perspective: It is the force acting per unit length along an imaginary line on the surface: $T=F/l$. Unit: N/m.
2. Energy Perspective: It is the work done (potential energy) per unit area to increase the surface: $T=W/\Delta A$. Unit: $J/m^2$. Since $1J=1N\cdot m$, $J/m^2=N/m$.