The integrand is highlighted, inside the ∫...dx, in the expression:
∫f(x)dx.{\displaystyle \int f(x)\,dx.}The whole expression is the integral over x of a real-valued function f(x). The integral sign ∫ represents integration. The dx indicates that we are integrating over x; x is called the variable of integration.

See Integral#Terminology and notation for more.
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