Individuals with Disabilities Education Act (IDEA): IDEA is a federal law ensuring services to children with disabilities throughout the nation. IDEA governs how states and public agencies provide early intervention, special education, and related services to more than 6.5 million eligible infants, toddlers, children, and youth with disabilities. Infants and toddlers with disabilities (birth-age 2) and their families receive early intervention services under IDEA Part C. Children and youth (ages 3-21) receive special education and related services under IDEA Part B.

Industrialized country or nation: A country or nation with a market economy comprising a significant portion of world production and trade markets.

Inflation: A rise in the general level of prices of goods and services in an economy over a period of time, which generally corresponds to a decline in the real value of money or a loss of purchasing power. See also Constant dollars and Purchasing power parity.

International Target Population: On the 2007 Trends in International Mathematics and Science Study (TIMSS), the International Target Population is all students enrolled in the grade that represents 4 years of schooling (for grade 4) or 8 years of schooling (for grade 8), counting from the first year of the International Standard Classification of Education (ISCED) Level 1 and providing that the mean age at the time of testing is at least 9.5 years (grade 4) or 13.5 years (grade 8). For most countries, the target grade was grade 4 or grade 8 or its national equivalent. All students enrolled in the target grade, regardless of their age, belong to the International Target Population. See also National Target Population and supplemental note 5.