That could be because investors believed that Fannie had a fundamental value such that buying below 90 cents per share made the stock too undervalued for investors to pass up. Or maybe a big investor had a buy operation that was building a position with a big limit order at or below 90 cents. Either way, the reasons for support don't matter to technical analysts; only the results do.
It all ultimately boils down to supply and demand for shares. That 90-cent level in FNMA is the spot where there's been an excess of demand for shares; in other words, it's a price at which buyers have been more eager to step in and buy shares at a lower price than sellers have been to sell. That big pocket of demand at 90 cents is significant, but it's important for traders to be reactionary. By actually waiting for a bounce off of support before buying, you're verifying that those buyers are still there before you put money on a trade.
On the other hand, a violation of support is a major signal that shares could be opening up to a lot more downside risk.
2. Trend Line Support
Support lines don't have to be horizontal, though. Another common form of support is trend line or trend channel support -- support that takes place along a trend line that's sloping. Take a look at the chart below to see an example.