a vineyard: an enclosed plot of ground planted with grapevines and worked for its grape harvest
A vineyard is the field, not the plant. The single grapevine is a different word (ἄμπελος), and open farmland in general is yet another (ἀγρός); this word names the whole tended plot of vines, usually walled or hedged, with a winepress and often a watchtower, worked season after season for its grapes.
Almost every time the word appears, it is inside one of Jesus's parables. The workers hired at different hours are sent into a vineyard, the two sons are told to go work in the vineyard, and the tenants who beat the owner's servants and kill his son are renting a vineyard. The one plain, non-parable use is Paul's everyday farming example: no one plants a vineyard without expecting to eat its fruit.
Because it stands at the center of so many parables, the vineyard carries a weight the bare word does not. Behind it lies the prophets' old picture of a vineyard the LORD planted and cared for and then looked to for fruit, a picture the Hebrew Bible applies to His own people. The Hebrew word for that vineyard (כֶּרֶם) is the one the Greek here regularly translates, so a reader who knows the earlier image hears it echoing whenever Jesus sets a story in a vineyard.