Major arc
= Major arc
In a circle-method problem of scale $n$, major arcs are neighborhoods of reduced rational points $a/q$ with small denominator, where the relevant <exponential sum> is approximated using distribution in residue classes. For the three-prime problem one may take $q\le(\log n)^B$ and $|\theta-a/q|\le(\log n)^B/n$, with suitably fixed $B$.