Company W sells products to consumers.

Company W buys materials from Company X$.$

Company $x$ buys materials from Company $Y.$

Company Y buys n$$aterials from Company Z$.$

According to the eTextbook Chapter $1,$ Company Z would be called Company W$\text{'}$s:

First$-$tier supplier

Second$-$tier supplier

Second$-$tier distributor

Third$-$tier supplier

First$-$tier distributor