This distinction is essentially one about the tempo of biological evolution. Microevolution manifests itself as continuous, small changes in gene frequencies within a population (phyletic gradualism). In contrast, macroevolution appears as sudden, gross changes in morphology and function that mark the emergence of a new species. It refers to two issues: the evolutionary origin and extinction of species, and the saltatory evolution of phenotypical features (punctuated equilibrium). In the past the Modern synthesis has been criticized for not being able account for macroevolution: it can account for changes or stabilities in gene frequencies within populations, but not for speciation. The response is that artificial selection experiments (e.g., with Drosophila flies) have not been continued long enough for a new species to emerge. If they were, then microevolutionary changes would eventually culminate in macroevolution. Furthermore, speciation is possible because within any gene pool one can find all those kinds of genetic differences that separate species. Conrad H. Waddington (1905-1975) referred to this as step-by-step Fabian evolution.
See Biological evolution, Evolutionary biology, Evolutionary developmental biology, Fisher’s theory of evolutionary mimicry, Modern synthesis, Phyletic gradualism and punctuated equilibrium, Speciation