An ambiguous term for a certain style of tabletop game, used pejoratively by critics and affectionately by fans. In the past, games designed for the American market often has several mechanics in common (thus the name) though the term has since become genericized to describe a certain kind of game. Though there is no set definition and many argue over whether a specific game counts as ameritrash or not, most agree that they have one or more of these traits:
Strong Theming
Most Ameritrash games are strongly built around a theme. Rather than just a background for the action, the theme inspires the gameplay itself. A fantasy game could have multiple playable races, each with unique abilities, while a game based on a movie or TV show might feature mechanics based on the show's characters or plot. As a more specific example, King of Tokyo is meant to emulate kaiju movies with the core gameplay consisting of attacking other monsters, destroying buildings, and fighting the military.
Moderate to Heavy Luck
Fairly subjective but a good rule of thumb is whether there is no randomness, simple roll-and-move, or whether nearly every action is dependent on the luck of the draw or roll of the dice.
Player Elimination
This one's fairly self-explanatory--it is possible to knock some players out of the game before it ends. In some cases, eliminating players is requirement for the game to end.
Direct Conflict or Zero Sum Gameplay
Where the advancement of one player comes at the direct expense of others. This can be in the form of combat, stealing, etc. By contrast, most Eurogames feature passive conflict which usually takes the form of auctions, negotiations, and resource denial.
Despite the name, these traits are not universally bad. Player elimination, for example, can be tolerable if games are short so the eliminated players aren't idle for too long. Direct conflict can be balanced by providing ways to bounce back quickly or to prevent opponents from piling on. Bad luck can be mitigated by providing many paths to victory. And theming? Well, I don't really know what's wrong with that.
Most of the old classics are considered ameritrash including Monopoly, Risk, and Axis and Allies. More modern ameritrash includes Cosmic Encounter, Space Hulk, Dune and Battlestar Galactica: The Board Game.