Amba (אמבה) is the pickled mango sauce that defines a sabich and shadows half the sandwiches on an Israeli street, a thick amber condiment built on fermented or brined unripe mango, fenugreek, turmeric, and chili. As a sandwich element it is not a filling but the load-bearing seasoning: the angle is that amba is doing the work a sauce, a pickle, and a spice blend would otherwise do separately, all at once, and it is assertive enough that the rest of the build has to be assembled around it rather than alongside it. A sandwich that uses amba is, in flavor terms, an amba sandwich first.
The character comes from how it is made and how little restraint it shows on the tongue. Sour unripe mango is salted and left to soften and ferment, then cooked or blended with a heavy dose of ground fenugreek, turmeric, garlic, mustard, and chili into a loose, ochre paste that is at once tangy, faintly bitter, savory, and hot. In the sandwich it is spooned or drizzled, not spread thick, because a little carries a long way. Its natural home is the sabich: pita stuffed with fried eggplant, hard-boiled or jammy egg, Israeli salad, hummus, and tahini, where amba is the thread that ties the soft egg and oily eggplant to the sharp salad. Done right, the amba is loose enough to thread through the filling and lands tangy and warm with the fenugreek present but not raw or chalky. Done wrong, it is pasty, bitter, over-poured so the whole sandwich tastes only of fermented mango, or so thin and timid it adds nothing. The bread, usually a fresh pita opened to a pocket, has to be soft and sturdy because amba and tahini together will turn a stale one to mush.
It travels well beyond the sabich. The same sauce goes into shawarma wraps, over falafel, alongside grilled fish, and onto a plain hummus plate for those who want it. It varies mostly by intensity and texture: some versions are smooth and mild with the fenugreek dialed back, others are coarse, fiercely sour, and heavily spiced; some lean on lemon and vinegar for the acidity, others on a long mango ferment. Each of those preparations is recognizable in its own right and deserves its own treatment rather than a line here, but they all return to the same idea: a single pickled-mango paste loud enough that the sandwich is designed around it rather than simply finished with it.