In the weed world, a hybrid is a cannabis plant with both indica and sativa characteristics. Because cannabis has been cultivated for centuries, most modern strains are hybrid strains. Landrace strains are traditional cultivars native to the region where they grow and are usually thought of as pure, non-hybrids. But even modern landraces have been relocated and domesticated. Pure sativas and pure indicas are fairly rare, so most cannabis you'll find these days is hybrid weed.
More about hybrid weed
Hybrid strains typically develop phenotypes that are either sativa-dominant, indica-dominant, or evenly balanced. Strain descriptions usually list it that way or display the split as a percentage. Remember that the terms indica strains and sativa strains are most useful for cultivators in determining growth characteristics like how tall plants will grow or how long their flowering cycle will be. Effects share no connection with the physical structure of today's cannabis plants.
Hybrid cannabis plants may also contain genetics from ruderalis varieties, a third type of cannabis that isn't dependent on light exposure to start flowering. Because ruderalis plants flower automatically based on how long they've been in the ground, they are often crossed with other cannabis plants so the offspring become “auto-flowering” varieties.