Short answers, pulled from the story.
The Nasdaq-100, or NDX, is a stock market index made up of equity securities issued by 100 of the largest non-financial companies listed on the Nasdaq exchange. It is a modified capitalization-weighted index that caps the influence of its largest components, with financial companies tracked separately in the Nasdaq Financial-100.
The Nasdaq-100 was launched on the 31st of January 1985 by the Nasdaq, alongside a companion index called the Nasdaq Financial-100. Its base price started at 250 and was later reset to 125 after the index closed near 800 on the 31st of December 1993.
The Nasdaq-100 is limited to non-financial companies from a single exchange, so banking, insurance, brokerage and mortgage loan companies are tracked instead in the separate Nasdaq Financial-100. Both indices launched together on the 31st of January 1985.
The Invesco QQQ is an exchange-traded fund that tracks the Nasdaq-100 and has been sponsored and overseen by Invesco since the 21st of March 2007. It traded as QQQQ on the Nasdaq from the 1st of December 2004 until the 23rd of March 2011, when Nasdaq changed its symbol back to QQQ.
As of January 2026, only four companies, Apple, Costco, Intel and PACCAR, have remained continuous components of the Nasdaq-100 since its first dissemination in 1985. KLA Corporation and Micron Technology were also original components but were removed from the index over time before later returning.
The Nasdaq-100 is rebalanced quarterly if one company reaches 24% of the index or if companies weighted at 4.5% or more together make up 48% or more of it. It is rebalanced annually, after the quarterly check, if one company reaches 15% of the index or the five largest companies together hold 40% or more of it. Nasdaq also carries out a full reconstitution of the index every December.