'Standard Average European,' in phonology and phonetics is a term used to refer to any language in the Indo-European language family that is typically (Western)European. The term is often used to contrast English with that is considered 'normal' for an Indo-European language, which all share some features of phonology and grammar.

Even non-Indo-European languages like Hungarian, Finnish, and the famous case of Basque appear to be SAE on the surface. In fact, if you don't pay close attention to the words, you can easily mistake Basque for Spanish because they sound similar, even though Basque is an extremely different language. The similar phonology of these languages to SAE languages is due to centuries of proximity to them.

English, on the other hand, is a rogue Indo-European language, due to its relative isolation in Britain and America (And to a lesser extent, Australia) and the fact that it is truly a melting pot of languages. It is a phonetic nightmare to anyone who didn't grow up speaking it, and a challenge to phonologists. Some of the main differences between English and SAE are the letter 'r,' the plosives, the alveolars, and of course, the vowels, illustrated here:

So, next time you consider making fun of a European's accent, remember that English is the one that's messed up, not them. Or, you could just make fun of them anyway, cause they are European afterall.

Of course, in a broader linguistic sense, this term is a grammatical one. It was coined by linguists studying Native American languages, notably Hopi, to point out the stark differences between the syntax of these languages and the syntax which is ingrained in any SAE language. For instance, things we take for granted such as past, present, and future are technically non-existent in some languages. Unfortunately, my area of expertise is in phonetics, phonology and historical linguistics, and I do not know much about the field of grammar and syntax. If someone knows syntax well, please feel free to add on to this write-up.