Deep Store

The Standard & Poor's 500 index. A cap-weighted basket of about 500 large-cap US stocks, widely considered *the* US equity benchmark. Adjusted close price from Yahoo Finance, so dividends and splits are accounted for.

Why it matters: When people say "the market," they usually mean this. ~80% of US market cap, correlated with every other major equity index, and the underlying for the deepest options and futures markets in the world.

How to read it: For long-term investors, the absolute price matters less than its percentile against historical valuation metrics (CAPE, earnings yield) and its trend relative to moving averages. The 200-day moving average is a common regime filter; price below 200DMA is generally considered a bearish regime.

Caveats: Because it's cap-weighted, it can be dominated by a handful of mega-caps — compare it to RSP (equal weight) to see how much of a move is broad-based vs. concentrated.