胡言乱语 is the full four-character idiom meaning 'to talk wild nonsense.' 胡言 alone is the shortened version with the same meaning.
history
胡 originally referred to northern nomadic peoples (胡人). 胡说/胡言 literally meant 'barbarian speech' - i.e. incomprehensible talk. The ethnic connotation has faded, and now it simply means 'nonsense.'
