喇叭 means 'horn / trumpet / megaphone' — anything that flares outward like a brass instrument. 喇叭裤 are 'horn-shaped trousers' — narrow at the knee, flaring out at the ankle. The metaphor matches English perfectly: 'bell'-bottoms vs. 'horn'-trousers.
history
In China, 喇叭裤 became a symbol of 1980s reform-era youth culture — initially controversial as 'capitalist decadence', then quickly mainstream. Wearing a pair was a small rebellion against the Mao-suit conformity of the previous decade.
