I've been asked this question several times in the past and I get why, because the two terms of pellet grill and pellet smoker often get used in the same instance/recipe and it gets people confused.

So your typical backyard horizontal pellet BBQ is both a grill and a smoker. It has the ability to cook food at lower indirect temperatures, say around 225 degrees, the typical temperature used to smoke foods. At that set temperature the pellet burn pot will be smoldering, hence you'll get smoke to give the food that nice smokey flavor.

However, when the temperature is set to 500 degrees plus, the pellet fire will be burning very efficiently to make sufficient heat. At this point, it becomes a pellet grill and very little smoke will be produced.

The only exception is vertical pellet smokers which look like a small cabinet. These are purely smokers and they cannot typically be set to a temperature over 400 degrees, hence they cannot grill/sear foods.