Two vectors of the same length are orthogonal if the sum of the products of their corresponding elements is 0. Note: An experimental design is orthogonal if the effects of any factor balance out (sum to zero) across the effects of the other factors.
This is a property of codes that can be used as spreading codes for direct sequence spread spectrum (DSSS) transmissions. Codes are said to be orthogonal if they sum to zero over a period of time. Orthogonal codes are used for DSSS transmissions because they do not interfere with one another.
A property exhibited between two PN codes whose cross-correlation, a mathematical measure of similarity, is zero. Orthogonality ensures that the two codes will not interfere with one another when present on the same communication channel.