For 1 ≤ p ≤ ∞, the Banach space of (real or complex) measurable functions f such that |f|p is Lebesgue integrable. The norm is given by
In Lp two functions that agree almost everywhere are considered equal; this is so that the norm property ∥f∥=0 implies f = 0 holds. When p = 2, then L2 is the space of square-integrable functions and is a Hilbert space.