What does "EW(Hα)" mean? I came across a website saying that classical T Tauris have an "EW(Hα) > 5 angstroms".

Does anybody know what "EW" means?

Thanks.
"EW" stands for Equivalent Width. The equivalent width of a spectral line is essentially the range of continuum one would integrate over to get the same flux as the spectral line.

In your case, this is the Hα line.