A stock index is a measurement of a section of the stock market. It is computed from the prices of selected stocks. Stock markets in both Canada and the U.S. have been experiencing volatility due to new tariffs. - The S&P/TSX composite index in Canada experienced significant declines, reflecting broader market anxieties. - U.S. stock markets also fell, mirroring the downward trend observed in the Canadian market. - Uncertainty surrounding U.S. tariffs on goods imported from Canada and Mexico is a key factor contributing to the market downturn. - The technology, energy, and base metal sectors in Canada were particularly affected by the market volatility.