I was talking about both -- for the purposes of explanation, frequency-hopping is more intuitive. (I was trying to be responsive to @Redfern above, who mentions

I was talking about both -- for the purposes of explanation, frequency-hopping is more intuitive. (I was trying to be responsive to @Redfern above, who mentions frequency-domain jamming.) Both frequency-hopping and direct-sequence spread energy over a larger bandwidth. Direct-sequence does not explicitly frequency-hop, but the time-domain switching it uses will spread the energy out in Fourier space.