Anthelmintic: A medication used to kill helminths, which facilitates their expulsion from the human body. The anthelmintics most commonly used to treat intestinal worm infections in children are the benzimidazoles (albendazole and mebendazole).

Coverage: The proportion of the target population reached by an intervention (e.g. the percentage of preschool-age children and school-age children receiving preventive chemotherapy on a treatment day).

Disability-adjusted life years (DALYs): A time-based measure which estimates the overall population-level burden of a particular disease caused by ill-health, disability or early death.

Elimination as a public-health problem: WHO defines STH as a public-health problem when >1% of the at-risk population has infection of moderate or high intensity. The goal is not to eliminate the parasites but to reduce the morbidity they cause to levels that can be controlled through routine healthcare or school-based services.

Endemic: The constant presence and/or usual prevalence of a disease or infectious agent in a population within a geographic area.

Hygiene: Conditions and practices that help to maintain health and prevent the spread of diseases. Hygiene practices include hand washing with soap, food hygiene, and environmental cleaning. 

Intensity of infection: The number of worms infecting an individual. The intensity of infection with soil-transmitted helminths can be measured directly, by counting the number of expelled worms after anthelminthic treatment, or indirectly, by counting the number of helminth eggs excreted in feces (expressed as eggs per gram [epg]). 

Morbidity: The clinical consequences of infections and diseases that adversely affect human health. Morbidity from STH is usually subtle (e.g. malabsorption, stunted growth) and proportional to the number of worms infecting an individual.

Neglected tropical diseases (NTDs): A group of diseases that historically has been overlooked. WHO is working to control, eradicate, or eliminate 17 neglected tropical diseases.

Preschool-age children (PSAC): Children aged between 1 and 4 years.

Preventive chemotherapy (PC): Use of anthelminthic as a public health tool to target simultaneously the prevalent helminth infections in the area.

Sanitation: The provision of facilities and services for the safe disposal of human excreta. It refers to the safe management of excreta from collection, emptying, transport, treatment and disposal or reuse.

School-age children (SAC): Children aged between 5 and 14 years who may or may not be enrolled in school. The exact ages of school enrollment may vary slightly in different countries. Because peak prevalence and intensity of Ascaris and Trichuris infection occur during this age range and because this at-risk population is easily accessed through schools, PC activities are often implemented through the school system. 
Soil-transmitted helminthiasis (STH): Infections in humans caused by a group of species of nematodes: Ascaris lumbricoides, Trichuris trichiura (the whipworm) and Necator americanus or Ancylostoma duodenale (the hookworms).

Soil-transmitted helminthiasis (STH): Infection in humans caused by a group of species of nematodes: Ascaris lumbricoides (roundworm), Trichuris trichiura (whipworm), and Necator americanus or Ancylostoma duodenale (hookworms).