Amid President Donald Trump's tariffs on multiple countries, U.S. stocks dipped low enough Monday to enter a territory known in industry parlance as a "bear market." Investor worries that a growing trade war will lead to higher prices and even a recession have caused stocks to fall sharply since last week, and it may not get better anytime soon. Trump and his administration − who have doubled down on the aggressive, sweeping tariff plan that has rattled markets for days − has indicated that even higher tariffs on dozens of nations are set to start Wednesday. After Trump's 10% tariff on all countries went into effect during the weekend, stocks fell at least 20% by Monday – plunging the U.S. into a bear market. Investors and financial analysts are well aware of bear markets and what such a situation could foretell for the economy. But if you've heard the term and wonder about its significance, here's a rundown of what a bear market is, what it could cause and how long it usually lasts. Tariff updates: Turmoil spurs more stock market struggles; Trump doubles down What is a bear market? A bear market is a stock market drop of 20% or more from a recent peak, or a closing high. That differs from corrections, which refer to drops of at least 10%. Traders work on the floor of the New York Stock Exchange in New York City, on April 7, 2025. Wall Street stocks opened sharply lower Monday, joining a global selloff on worries that a trade war induced by US President Donald Trump's tariffs will spark a global economic slowdown. It's also the opposite of a bull market, which is one in which stocks have gone up. Last week, the Dow posted back-to-back losses of more than 1,500 points for the first time ever, including a 2,231-point freefall on Friday. On Friday, the S&P 500 posted its biggest one-day loss since March 2020, the start of the COVID-19 pandemic, and Monday morning tumbled into a bear market. The tech-heavy Nasdaq was already in a bear market. The term most often refers to the S&P 500's performance, which is generally considered a benchmark indicator of the entire stock market, according to the Motley Fool, a financial and investing advice company. However, a bear market can also refer to any stock index or individual stock. Bear markets can sometimes serve as precursors to recessions, though that's not always the case. A recession is informally considered to be at least two straight quarters of declining economic output, based on employment, income, consumer spending and industrial production, among other criteria. What causes bear markets? U.S. President Donald Trump delivers remarks on tariffs, in the Rose Garden at the White House in Washington, D.C., U.S., April 2, 2025. REUTERS/Leah Millis Bear markets tend to happen when investors are feeling particularly pessimistic about the future of the economy. While the specific reason for a bear market can vary from era to era, they happen when investors worry corporate earnings will tumble and drive down companies' overall value. Get enough of these reeling valuations together in a group of stocks such as the Standard & Poor's 500, and you could end up with a bear market. The current bear market was sparked over worries that Trump has ignited a trade war that will lead to higher prices and recession. How long do bear markets last? Though some have been as short as a few months, bear markets can last as long as a couple of years. That's much longer than the four or so months it takes on average for the stock market to recover from a less severe correction, defined as a 10% to 19.9% decline from a recent peak, according to investment research and analytics firm CFRA Research. When was the last bear market? A bear market occurred in 2022 amid investor fear that the Federal Reserve's attempts to bring inflation down from a 40-year high would slow the economy too much, sapping consumer spending and business profits. There was also one amid the COVID-19 pandemic in 2020 as U.S. indexes dove at record speed into bear markets due to the ensuing global shutdown. Since 1929, there have been nearly twice as many bear markets as recessions in the United States. Nine of those bear markets occurred around the Great Depression and the recession that followed. While recessions don't always follow a bear market, Bankrate Chief Financial Analyst Greg McBride said, "the speed of the decline since Thursday morning is unique, and is particularly unsettling. Investors should resist the urge for the knee-jerk reaction of selling." Contributing: Bailey Schulz, USA TODAY This article originally appeared on USA TODAY: What is a bear market? Trump tariffs caused one as stock market dips