from Wittwer CT and Farrar JS (2011) in PCR Troubleshooting and Optimization

Real-time PCR not only automates both amplification and detection, but integrates them so that they occur concurrently. Time, temperature and fluorescence are monitored during PCR in real-time instruments. The earliest report of continuous monitoring of PCR and acquiring fluorescence at each cycle utilizing ethidium bromide, a double-stranded DNA (dsDNA) specific dye. This allowed for a truly homogenous or "closed-tube" assay in which product amplification was combined with detection. The most important application of real-time PCR is quantification of the initial template, known as quantitative PCR or qPCR (Wittwer and Farrar, 2011 in PCR Troubleshooting and Optimization).