Company W sells products to consumers.

Company $W$ buys materials from Company $x.$

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

Company $Y$ buys materials from Company $Z.$

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

Second$-$tier supplier

Third$-$tier supplier

First$-$tier supplier

First$-$tier distributor

Second$-$tier distributor