The word bar has several common meanings:

1. A solid piece of material, usually longer than it is wide. A bar of soap sits by the sink. Prison windows have metal bars to prevent escape. Gymnasts swing from bars in competition. When you see gold bars in a vault, you're looking at rectangular blocks of pure gold. A chocolate bar is a similar rectangular shape you can hold and eat.
2. A counter where drinks are served, or the establishment containing it. At a bar, customers sit on stools and order beverages. The bartender works behind the bar, mixing drinks and serving customers. Some bars serve food as well. A juice bar serves healthy drinks instead of alcohol.
3. Something that blocks or prevents. When someone says “language should never be a bar to friendship,” they mean language differences shouldn't prevent people from becoming friends. If rules bar you from entering a contest, those rules keep you out.
4. A unit of measurement for pressure, used especially in weather forecasting and scuba diving.

The phrase “raise the bar” means to set a higher standard. If your science project raises the bar for the whole class, you've created something so impressive that everyone else now has to work harder to match it.