Final answer:
A semi-automatic weapon fires one round with one trigger pull, while a fully-automatic weapon can continuously fire rounds as long as the trigger is held down.
Step-by-step explanation:
In the context of firearms, a semi-automatic weapon is one that fires one round with one trigger pull, ejects the used cartridge case, and loads a new round into the chamber automatically. However, the shooter needs to pull the trigger for each round fired. On the other hand, a fully-automatic weapon is capable of continuously firing rounds as long as the trigger is held down, until the ammunition is depleted. These weapons can fire multiple rounds with a single trigger pull.
For example, an AR-15 rifle that is commonly used in the United States is a semi-automatic weapon. Each time the shooter pulls the trigger, it fires one round. Conversely, a machine gun is a fully-automatic weapon that can fire multiple rounds with a single trigger pull without the shooter needing to manually operate the firearm for each round. An example of a fully-automatic weapon is the M16 rifle used by the U.S. military.