red cap; red hat
Literal meaning: a cap or hat that is red in color. Can refer to any red headwear, but often associated with the uniform of railway porters.
A person wearing a red cap carried my luggage at the station.
railway porter; redcap
By metonymy, a porter at a railway station who traditionally wears a red cap as part of the uniform. This usage is somewhat dated but still understood.
In the past, there were redcaps at stations who carried travelers' luggage.
Compound of 赤 (あか, 'red') and 帽 (ぼう, 'hat' or 'cap'). The porter sense derives from the red caps worn as part of the uniform.