Macgyverism is an ingeniously improvised solution to a problem, assembled out of whatever happens to be within reach rather than out of the right tool for the job.
The word is a coinage rather than standard vocabulary: no major dictionary carries it, and Wiktionary is the reference that records it, listing it as both countable and uncountable with the plural MacGyverisms and attesting it in print by 2005 in Make magazine. Casing is unsettled in the wild. Wiktionary lemmatizes the form that preserves the character's internal capital, MacGyverism, while the flattened Macgyverism used here also circulates widely; both refer to the same thing, and neither has an authority behind it strong enough to rule the other out.
It comes from 📝MacGyver, the American television series that ran from 1985 to 1992, whose secret-agent protagonist resolved crises by applying scientific knowledge to ordinary objects — paper clips, duct tape, chewing gum — instead of to weapons. The formation is the character's surname plus the suffix -ism, which makes the word a working example of an 📝eponym in its second sense: a proper noun worn down into a common one for the thing it named. The back-formed verb to MacGyver follows the same path and is now the more common of the two.
A Macgyverism is not a kludge. Both name a fix built from the wrong materials, but a kludge is judged by its inelegance and a Macgyverism by the ingenuity that constraint forced out of the maker — the term is close to unusable as an insult. The constraint is load-bearing: the improvisation counts only because the proper tool was unavailable.