"A couple" is two. "Several" is more than two but less than many. "A few" is the lower end of several. So; none, one, one or two, a couple, a few, several, many.
"Is" ? Words are not like that. Meanings always come first, words follow. However, a problem occurs in the ongoing evolution of a language as there are never enough words available to describe the number of meanings which can arise. Which is why there may be multiple 'definitions' of a word within dictionaries. (Incidently, the field within a dictionary page which is called the 'definition' of a word actually contains
descriptions of how a word has been used, and is currently being used.) Dictionaries (with one of two exceptions - legal and so forth) never 'define' words, but instead follow in the wake of their current useage(sic), by describing those useages(sic).
The origins of the word 'couple' had nothing whatsoever to do with two - it was the Latin word
copula meaning 'to tie' or 'to connect'. We still use the word in this sense of course, when talking about the 'coupling' of railway carriages. It was a word used to describe an action rather than a quantity.
It was not until the late 13th century that the French word
cople evolved from it to specifically describe a 'married couple or lovers'. The meaning was later broadened in the 14th century to describe 'any two things'.
Sure, these days many people use the word 'couple' in the 13th/14th century sense of 'two', or 'a pair', but the meaning of the word is not static (it never has been) and these days it is often used to mean a few, or an undefined small number - as in: "knock a couple (i.e. a few) more nails in", or "it cost more than a couple of quid", for example.
The meaning of words continues to change (along with their spellings), and thus 'IS-ness' therefore cannot ever apply. Which irritates pedants no end, as they continually seek to live within a static, unchanging world which provides them with that same illusion of safety, stability and security to be found within any child's comfort blanket.
LJ