Direct sequence spread spectrum
is a technique for sending a radio signal from a transmitter to a receiver.
It uses one or more channels. Each channel contains a section of the original signal, which is sent along a frequency channel to improve reliability of reception.
Additionally, on each frequency, a 'chipping code' is used. This is a essentially a non sinusoidal carrier signal. Because the chipping codes are orthogonal this can actually can allow more than one user to transmit at the same time on the same frequencies with only a minor increase in noise to each user, up to the limit described by Shannon's law.
The end result is that spread spectrum radio can be difficult to intercept and jam, and further it is relatively immune to multipath distortion.