A bugle is a kind of brass instrument. A lot like a trumpet but without valves/fingerstops. Its played (I think) by pursing the lips, blowing a kind of rasberry into the mouthpiece to make the sound and changing the shape of the cheeks to somehow alter the pitch of the note - not entirely sure how this works!
If you watch movies which are set in Medieval time I think it, or something very similar, can be seen in these. They used an extended version of the bugle, which I don't know the name of.
I think its also the instrument that is played at army funeral services - the Last Post I think?