what"s the word? voltage back-flow protection? (can I get a better word for that? it"s slipping my mind)
We generally call it "reverse current protection" on this side of the pond, which also covers Murphy"s Law situations like customers inserting batteries backwards (despite preventive mechanical alignment and labeling precautions), connecting cables incorrectly, etc. One way to remember is that current is a measure of electron flow quantity, and voltage is a measure of potential difference (analogous to fluid flow and pressure in fluid mechanics terms).
The best things in life aren't things ... but, a Pi comes pretty darned close!
"Education is not the filling of a pail, but the lighting of a fire." -- W.B. Yeats
In theory, theory & practice are the same - in practice, they aren't!!!