The product of a number and its reciprocal equals 1.
The reciprocal of 4 is 1/4.
The reciprocal of 2/3 is 3/2.
The reciprocal of 1 is 1.
The number 0 does not have a reciprocal because the product of any number and 0 equals 0.

The reciprocals of a number is sometimes called the Multiplicative Inverse of the number.

The product of a negative number and its reciprocal equals 1. If the number is negative then the reciprocal must also be negative to produce a product of +1.
The reciprocal of -4 is -1/4.
The reciprocal of -2/3 is -3/2.
The reciprocal of -1 is -1.