Complex sentence: The word "steel" comes from a piece of polished steel, also called a "tonebar" that is held against the strings and moved horizontally to change the pitch, which gives the infinite slide, or portamento, that is so characteristic.
Split into simpler sentences: The word "steel" comes from a piece of polished steel, also called a "tonebar" that is held against the strings and moved horizontally to change the pitch. This gives the infinite slide, or portamento, that is so characteristic.