referir(se) = to refer
'referido' is the past participle
'referred' as simple past (I referred, etc.) chnages according
to:
yo referi - I referred
tu referiste - you (singular, informal) referred
usted/el/ella refirio - you (singular, formal)/he/she
referred
nosotros referimos - we referred
vosotros refireis - you (plural, informal) referred
ustedes/ellos/ellas refirieron - you (plural,
formal)/they(male/female) referred.