What the 5% significance level actually promises

A research desk uses the usual 5% significance level ($\alpha = 0.05$) for every test. Suppose they run this exact test on 200 candidate strategies that, unknown to them, all have zero real edge (the null is true for every one).

About how many of these 200 dead strategies will still come back flagged as "statistically significant," and what does that number tell you about the meaning of $\alpha$?