The term 'REALLY SEXY' can be broken down into two words, 'HOT' and 'SEXY'. The word 'HOT' is a three letter word that means having or giving off heat, having a high degree of intensity, or being very attractive. The word 'SEXY' is an adjective that describes someone or something that is sexually attractive or exciting. Together, the two words form the phrase 'REALLY SEXY', which is used to describe someone or something that is extremely attractive or exciting.