The large-scale structure of the Universe can only be observed directly via luminous tracers of the underlying matter density field. However, luminous tracers, such as galaxies, do not precisely mirror the clustering statistic of the bulk of the cold dark matter distribution: their correlation function (or power spectrum) is biased and depends on various properties of the tracers themselves. Although on small scales this bias is an unestablished function of space and time, on very large scales it results in a constant offset in the clustering amplitude, known as linear bias. In this talk we focus on the bias of luminous objects within and around cosmic voids, enormous under-dense regions of the Universe that occupy the vast majority of its volume. As a remarkable result, we find that, within voids, the relation between matter and galaxy density is always linear and determined by a multiplicative constant. Furthermore, the value of this constant decreases with the increase of the size of voids and asymptotes to the linear bias. This result opens to the possibility of using such simple relation in other voids studies, allowing to extend our theoretical understanding of voids (typically defined as depressions in the matter density field) to voids that are identified using galaxies as tracers of the matter density. Ultimately we aim to test these possibility with observations, using the Dark Energy Survey data currently available.