Since players get gold and experience points for killing an enemy hero, bad mannered players who want to ruin a game for their own team will repeatedly run down the middle lane to feed gold and experience to the enemy team, allowing them to win faster. It looked like the AI was doing that, but other people who played against the AI said it's more like a last ditch effort to try and keep the enemies out of their base when the AI doesn't know what to do when it's on the verge of losing.

dx87 gave a good explanation.

"Feed" is a term in Dota when players (aka Heroes) die without any benefit to your team--such as destroying an enemy spawn (racks/Barracks), killing another team Hero (hopefully more one). It's "feeding" as the other team members nearby will get gold and experience for each kill. As there is a respawn timer, the character who is dead will not get Exp nor Gold during that count-down resulting in a character that is disadvantaged as it will be under leveled compared to the rest of the heroes.

In the early and mid games of Dota, not gaining experience and gold is a major setback. Dying has a huge penalty.

The term "feed" is used with players who are learning the game, or those who are low skilled, and are haven't yet mastered some of the main aspects of playing. They're dying with no benefit, boosting the other team.

"Mid" simply means 'middle lane.' DOTA has 3 lanes, top, middle, and bottom, and short hand refers to them as top, mid, bot, respectively.

If your team is losing, boosting the other team to get the game over with is poor sportsmanship. A single team battle could easily shift the game into the losing teams favor.

In sports like Football, you may see teams pull their starters to 1. prevent injury and 2. give other teammates experience, but you'd never see someone purposefully help the opposing team win.