1A machine used to calculate and receive payment at checkout; short for レジスター (register).
レジで会計を済ませてから店を出た。
I paid at the register and then left the store.
新しいレジを入れてから、会計がずいぶん速くなった。
Since installing the new register, checkout has become much faster.
2The checkout counter itself, or the staff member working there.
夕方はレジが混むので、早めに買い物を済ませた方がいい。
The checkout gets crowded in the evening, so it's better to finish shopping early.
彼は大学生の頃、コンビニのレジのアルバイトをしていた。
When he was a university student, he worked part-time as a cashier at a convenience store.