Synaesthesia as a word and concept cannot be fully explained by an absolute characterization. This is precisely because this concept is a marvel of the human senses.
an involuntary and automatic response
It is worth mentioning the fact that there is only a small percentage of people who are possessed by this rare feeling, below we will make a reference to the general population and what this feeling creates.
Synaesthesia is a neurological condition in which the brain has the ability to connect sensations that in any other case would have no relation to each other. An example would be someone who is listening to music seeing a colour, or someone who is tasting a food hearing a sound. People of this type associate colours with tastes, i.e. red tastes sweet, yellow tastes sour and so on. Someone with synesthesia could literally taste the rainbow by seeing its colors!
According to Harvard Medical School, only 1% of people have synesthesia and that includes Marilyn Monroe and Pharrell Williams.