Taboo words are those that are considered in bad taste by some people or that are better to be avoided because they mention realities that are stark or vulgar. They refer to sex, religion, necessities such as the act of emptying the bladder or the bowels, and so on. Examples: fuck, fornicate, masturbation, prick, cunt, the devil, crap, piss, die, etc.
The taboo is a social phenomenon; some terms are therefore regarded as taboo by some people, but not, by others. Let us take the weasel as a case in point. We have a lovely animal in principle, but a farmer may think otherwise because if it eats his chicks and his hen's eggs, he will scream blue murder by the sole fact of hearing its name. Extremely religious people find it impure to speak about things in which blood is involved: labour (birth), menstruation, etc.
A euphemism is the replacement of a taboo expression by another that is not coarse. Euphemisms try to conceal the reality that lies behind. Instead of "fuck" or "fornicate", we use "make love"; of "prick" or "cunt", "private parts"; of "the Devil", "the Evil One"; of "crap" or "piss", "go to the toilet / loo", etc.
Euphemisms can even make the harsh reality appear natural, which is why they are used by politicians in order to take the people in and endear themselves to the public: neutralise (= kill, murder). It is not the same to say: The natives have been neutralised as to say: The natives have been exterminated / massacred / killed. The reality is the same, but not the way to express it, and the effect that it produces.
Dysphemisms consist in employing disparaging or negative terms to describe people, things, facts, etc. We make use of them to deride the person, thing or fact referred to and there may be a humorous tone: poetaster, old banger (to talk about a luxury car), and so on and so forth. They can also be cruel: Last night that thing (= my mother's boy friend) came home to have dinner.