Tuff
In a volcanic eruption, Magma is blown apart by volcanic gases and steam.  The products are volcanic gases, lava, steam, and tephra (fragments).  The solid material produced and thrown into the air is called tephra, regardless of composition or fragment size.  If the pieces of ejecta are small, the material is called volcanic ash, defined as such particles less than 2 mm in diameter, sand-sized or smaller.  These particles are small, slaggy pieces of magma and rock that have been tossed into the air by outbursts of steam and other gases.