Nvidia (NASDAQ: NVDA) stock is falling in Tuesday's trading. The artificial intelligence (AI) leader's share price was down 5.5% as of 2:45 p.m. ET amid a 0.9% decline for the S&P 500 index and a 1.6% pullback for the Nasdaq Composite index.

Chipmaker and AI darling Nvidia is back nipping at Apple's heels as the most valuable company in the world, with the stock hitting an all-time high Monday.

NVIDIA (NASDAQ: NVDA) is still the most important stock after two-plus years of dominating the stock market. Its GPU technology unlocked the door to AI, and now NVIDIA is capitalizing on it using a full-stack method.

Nvidia sells graphics processing units (GPUs) that provide computing power for various uses. More than two decades ago, the main function was to support PC gaming. But what has put the business on the map in recent years has been its GPUs that enable training AI models in massive data centers, now representing the bulk of the chipmaker's sales.

Investors are always scanning the horizon for the next big thing in stocks. For the past few years, it's clear that Nvidia (NASDAQ: NVDA) has been the key winner that's driven most index (and portfolio) returns.