To give it its full title "contribution" is "contribution to fixed costs and profit".
In other words, the excess of revenue over variable costs first goes towards covering the fixed costs - at the point at which this excess = fixed costs is the point of breakeven - and, thereafter, any further excess will be profit.
The foundation of breakeven analysis is that:
Sales revenue - variable costs (i.e. Contribution) = Fixed costs at the point of breakeven
In other words, the excess of revenue over variable costs first goes towards covering the fixed costs - at the point at which this excess = fixed costs is the point of breakeven - and, thereafter, any further excess will be profit.
The foundation of breakeven analysis is that:
Sales revenue - variable costs (i.e. Contribution) = Fixed costs at the point of breakeven