Minecraft wiki entry for Target_selectors, associated text: Examples in Java Edition:
@e[x=1,dx=4,y=2,dy=5,z=3,dz=6] — Select all entities whose hitbox collides with the block region (1~5, 2~7, 3~9) (or, mathematically speaking, the region that is {(x,y,z)∈R3|x∈[1.0,5.0),y∈[2.0,7.0),z∈[3.0,9.0)}).
@e[x=1,y=2,z=3,dx=0,dy=0,dz=0] — Select all entities whose hitbox contains the point (1,2,3).