Tariff
A tariff is called an optimal tariff if it's set to maximize the welfare of the country imposing the tariff. It is a tariff derived by the intersection between the "trade indifference curve" of that country and the offer curve of another country. In this case, the welfare of the other country grows worse simultaneously, thus the policy is a kind of "beggar thy neighbor policy". If the offer curve of the other country is a line through the origin point, the original country is in the "condition of a small country", so any tariff worsens the welfare of the original country.
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.