Sexual conflict

Sexual conflict is a term in evolutionary biology. It occurs in a species when what benefits the females is different from what benefits the males.
The word 'benefit' here means 'what benefits the reproduction of the female's (or male's) genes. It is expressed as a "difference in biological fitness".
The conflict can lead to an evolutionary arms race between males and females. It has primarily been studied in animals, though it can in principle apply to any sexually reproducing organism, such as plants and fungi.
Fundamental difference of interest.
In sexual reproduction there is, from the point of view of evolution, a fundamental difference of interest between males and females. This difference of interest plays out differently in different species.
Their interest is to mate with a large number of completely faithful females, thus spreading their genes widely in the population.
Their interest is to mate with a large number of fit males, thus producing a large number of fit and varied offspring.
Examples.
Some regard sexual conflict as a subset of sexual selection (which was traditionally regarded as mutualistic), while others suggest it is a separate evolutionary phenomenon.