As Native Latvian speaker I can tell you that translating it directly Lidpasts would be "Flying Mail" in other words "Air Mail".
If stamp would have another town not Riga, for example "Liepaja Lidpasts" would be more desirable stamp, but considering that Country has been thru Russian occupation from 1939- 1941 then German occupation 1941 - 1945 and then Russian occupation from 1945 - 1991 this stamp has seen a lot :) In Riga this stamp would be worth next to nothing. More desirable ones are original first stamps which are printed on a original ww1 German military maps due to the paper shortage.

Or for example Latvian 1930s airmail stamps are very desirableSad story is I do not collect Latvian stamps, I am into American ones
