Tariff
A tariff is a tax on imports or exports between sovereign states. It is a form of regulation of foreign trade. It is a policy that taxes foreign products to encourage or protect domestic industry. It helps limit trade deficits. The tariff is historically used to protect infant industries and to allow import substitution industrialization.
Tariff-rate quota
In a TRQ, the quota component works together with a specified tariff level to provide the desired degree of import protection. Essentially, a TRQ is a two-tiered tariff. The first Q imports entering within the quota portion of a TRQ are usually subject to a lower tariff rate called the Inside tariff quota rate or ITQR. Imports above the quota's quantitative threshold (Q) face a much higher (usually prohibitive) Outside tariff quota rate or OTQR. The Q units are called the quota volume, and this volume serves as the cut off between the ITQR and the OTQR.