Barrels are a type of container with potential treasure inside. However, many barrels explode when smashed open, dealing slight damage. These explosions are not traps that will emit a triggering sound before detonating, they explode instantly and are unavoidable.
Barrels often are grouped together, and when one explodes, it will also detonate any other explosive varieties standing immediately adjacent to it.
The loot they drop, if any at all, is generally not very good and with their high chance to explode, they may not even be worth the effort.
In Act V, there is a different type of barrel. These stone barrels are usually not found in groups, and while they do still frequently explode, they do not inflict any damage.
Baskets and Crates are like barrels in that they are kicked apart to open. They do not explode, however, but can be trapped.