In Wagner’s “Rule, Britannia”, the orchestration calls for two trumpets.
Vent. is an abbreviation for Ventil, which is the German for valve.
Ord. probably denotes ordinary, for non-valved trumpets, i.e. bugles.
If you look through the Vent. parts, they do feature chromatic notes, which would require valves. The Ord. parts are all bugle notes, except these bugles have a lowest open note which is an octave lower than today's common D trumpet.