In spite of being widely available passata maintains a certain air of mystery. According to the article on OChef:
The bottle in my pantry (Italian) appears to be of the uncooked variety. . . we looked through more than 30 major Italian cookbooks and reference books, and guess what? No recipes whatever. Our leading food dictionaries have no entries, . . .
Finally, we came across two British books A Cook's Guide to Italian Ingredients (Canada, UK) and La Cucina Italiana (Canada, UK) that seemed to agree on a definition for passata: "sieved red tomatoes." Depending on the degree of sieving, the pulp can be perfectly smooth (polpa di pomodoro) or slightly chunky (passata rustica). So passata - at least according to some Brits - is skinned, seedless, unflavoured, uncooked tomato pulp, either slightly chunky or smooth.