Software Defined Radio
Computers and amateur radio have a long history. Computer-controlled radios are ubiquitous and digital modes are becoming more and more a part of RF communication. Software-defined radio is another way computers are intersecting with radio.
SDRs are devices where software replaces some portion of the signal-processing chain traditionally performed by hardware. One could also say that SDRs perform digital signal processing on radio waveforms.
It is important to differentiate computer-controlled radios from software-defined radios. Most computer-controlled radios are traditional radios that allow the operator to use a computer (rather than inputs on the radio) to select frequency, toggle filters, and perform other actions.