The first three terms are the renormalized kinetic, mass, and quartic interaction terms. The remaining three are <counterterms>: $\delta Z$ gives <wave-function renormalization>, $\delta m^2$ renormalizes the mass, and $\delta\lambda$ renormalizes the four-point coupling. With all momenta entering a vertex, the momentum-space <Feynman rules> are
$$
\text{propagator: }\frac{i}{p^2-m^2+i0},
\qquad
\phi^4\text{ vertex: }-i\lambda,
$$
$$
\text{two-point counterterm: }i(\delta Z,p^2-\delta m^2),
\qquad
\text{four-point counterterm: }-i\delta\lambda,
$$
together with momentum conservation at every vertex and an integral $\int d^dp/(2\pi)^d$ for each independent <loop momentum>.

Solution

Past exam of the mathematics course of the University of Cambridge / 2024 / iii / Paper 304 / 2 / a / Solution

A loop momentum is an independent momentum integrated over in a <Feynman diagram>. Momentum conservation leaves one independent loop momentum for each cycle counted by the <loop order>.

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 Incoming links: Loop momentum