Grenadier is a type of soldier who used to be really important a long time ago. They would dress up in special outfits and carry weapons called grenades - these are like little bombs that explode when they're thrown.
Back in the olden days, before we had fancy guns and things, throwing grenades was an important part of fighting in battles. These soldiers would throw grenades at their enemies to try and hurt them or even blow them up.
Nowadays, we don't use grenadiers as much anymore, because we have more advanced weapons that can do the same job. But they still hold a special place in history as brave soldiers who were willing to put themselves in danger to protect their country.