Meaning: the Latinized form of Greek Meleagros, composed of Greek elements melas (black, dark) and agros (land, field) meaning "black land" or "black field", likely in reference to burnt farmland in order to make the soil more fertile.
I've also seen it listed as coming from Greek meleos (unhappy) meaning "unhappy land".
In Greek mythology, Meleager was the son of Althaea and Oeneus, the king of Calydon (though some versions put him as the son of the war god Ares). When he is born, the Fates tell his mother that Meleager would live only if a piece of wood burning in the family hearth would be completely consumed by the fire. Althaea immediately douses the flame and keeps it hidden safely. Many years later, when Oeneus forgets to pay tribute to the goddess Artemis she sends the Calydonian boar to terrorize the kingdom. Meleager and many powerful warriors banded together to kill it, including the warrior and huntress Atalanta, with whom Meleager was in love with. When the boar is killed, he offers its hide to her to the other men's protests, and when they tried to take it from her Melegaer killed them- his uncles, his mother's brothers. When Althaea heard this, she took out the log of wood and threw it into the fire and when it was burned up he died, just as the Fates foretold. Those who mourned him were turned into guineafowl, which is how it got its scientific name Agelastes meleagrides, because when he died his sisters cried so much that Artemis turned them into guineafowl, known as the meleagrids.
Meleager is also mentioned as being one of the Argonauts. When Heracles went down into Hades to capture Cerberus as part of his 12 labors, Meleager is the only shade who does not flee from him. He tells Heracles his story, including his unmarried sister Deianeira, and entreats him to take her as his bride- which he does, resulting in his death later on.