8 terms defined in plain English, each with a link to articles that use it.
Xaxa Committee
The Xaxa Committee was a High Level Committee set up by the Prime Minister’s Office in August 2013 under Professor Virginius Xaxa to study the socio economic, health, and educational status of tribal communities in India. Its May 2014 report found that tribes, about 8.6 percent of the population, remained among the poorest and most marginalised, and made 111 recommendations on land alienation, livelihoods, and service delivery. It is a key reference for questions on tribal development.
Example: The committee recommended empowering gram sabhas to restore alienated tribal land to its original owners.
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XENON
XENON is a series of dark matter direct-detection experiments at Italy's Gran Sasso National Laboratory, run by an international collaboration. The current detector, XENONnT, uses a multi-tonne dual-phase time-projection chamber of ultra-pure liquid xenon, shielded 1,400 metres beneath the Gran Sasso mountain to screen out cosmic rays, and hunts for the faint flashes produced if hypothetical weakly interacting massive particles (WIMPs) collide with xenon atoms. It has set world-leading limits on dark matter candidates and, because of its record background purity, is also opening a new window on solar neutrinos.
Example: In 2026 the XENONnT collaboration reported the first observation of low-energy solar neutrinos scattering off electrons in the detector.
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xenotransplantation
Xenotransplantation is the transplantation of organs, tissues, or cells from one species to another, and is actively researched as a way to address the severe shortage of human donor organs for patients with organ failure. Pigs are the preferred source because their organs are similar in size to humans' and they can be genetically modified to reduce immune rejection, which is the main barrier to success. It remains experimental and raises ethical and biosafety questions about cross-species disease transmission.
Example: In January 2022, surgeons in the United States transplanted a genetically modified pig heart into a human patient, marking a landmark first in xenotransplantation.
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xerosere
A xerosere is the sequence of ecological succession that begins in a dry habitat, such as bare rock or sand, and progresses through stages of increasing vegetation cover toward a stable climax community. Pioneer species such as lichens and mosses colonise the bare surface first, gradually building up soil until drought-tolerant herbs, shrubs, and finally xerophytic trees establish. It is the dry-condition counterpart of the hydrosere, which begins in water.
Example: Lichens and mosses colonising bare rock and slowly forming a thin soil layer that later supports hardy shrubs is a classic xerosere.
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Xinhai Revolution
The Xinhai Revolution is the 1911 revolution in China that began with the Wuchang uprising of 10 October 1911, overthrew the Qing dynasty and ended two millennia of imperial rule with the Republic of China of 1912.
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XPoSat (X-ray Polarimeter Satellite)
XPoSat (X-ray Polarimeter Satellite) is India's astronomy observatory launched 1 January 2024 to study black holes and neutron stars; it made India the second country after the US to fly a dedicated X-ray polarimetry mission.
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Xuanzang
Xuanzang (602-664 CE) is the Chinese Buddhist pilgrim who travelled to India between 629 and 645 CE during Harshavardhana's reign, studied at Nalanda under Shilabhadra, and carried hundreds of scriptures back to China. His Great Tang Records on the Western Regions (Si-Yu-Ki) is one of the richest foreign accounts of 7th-century India. For UPSC his testimony on Nalanda, Harsha's administration and contemporary society is a staple source-based question.
Example: His description of Nalanda as a great monastic university housing thousands of monks and students.
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Xuanzang (Hiuen Tsang)
Xuanzang was the Chinese Buddhist pilgrim who travelled across India from 629 to 645 CE, studying at Nalanda and attending Harsha's court at Kannauj. His account, the Great Tang Records on the Western Regions (Si-yu-ki), is a priceless source on seventh-century Indian society, polity and Buddhism. For UPSC, he is a staple ancient-history topic alongside Fa-Hien, and his writings illuminate Harsha's reign and Nalanda's glory.
Example: Great Tang Records on the Western Regions (Si-yu-ki), c. 646 CE
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