Tephra
Tephra is the rock, ash, and debris that a volcano throws into the air during an eruption.
Think of it this way
A volcano works like a pot of oatmeal boiling too fast on the stove. Hot steam builds up and blasts thick oat bits into the air. The chunks and fine dust fly out and land all around the pot. That scattered mix of oat pieces and powder is tephra.
Explaining tephra by grade level
A volcano can blast rocks and ash high into the sky. These bits of rock are called tephra. Some pieces are tiny like dust. Others are as big as your fist.