It's "Economy Light" in Lufthansa-speak.

It is quite confusing. Light gets you miles but not changability for a fee or checked bags. S class originating from the US is supposed to have these restrictions, or at least the possibility of these restrictions. If you have a point of origin in the US, the W basis is not supposed to have baggage restrictions. However, I had a W and it did. I needed to upfare to a V.