This question was asked today by “Rambabu26 d” and it has been answered by three chromatography wizards.

Bullfrog21, who gave a short but precise answer:

Peak width is the distance on the graph between the two lowest points on either side of the peak. […]

A second answer came from, T0bl3rone who assumed that the question was about TLC (Thin Layer Chromatography) or perhaps never dealt with a modern column chromatography that gives results in a form of a plot of detector’s response over time – chromatogram:

I don’t know what u mean by peak width. Is it Rf value that you mean?
Rf value is the comparison between “the length from base line to the ink spot” to the length from the base line to the solvent front”
Base line is the line where you put your sample.
Solvent front is where you stop the chromatography activity […]

and finally a more comprehensive answer by Surendrabateja, a top contributor who answered more than 550 questions:

Peak Width :
Generally chromatographic data is presented as a graph of detector response (y-axis) against retention time (x-axis). this provides a spectrum of peaks for a sample representing the analytes present in a sample eluting from the column at different times. Retention time can be used to identify analytes if the method conditions are constant. Also, the pattern of peaks will be constant for a sample under constant conditions and can identify complex mixtures of analytes.

The area under a peak is proportional to the amount of analyte present. By calculating the area of the peak using the mathematical function of integration, the concentration of an analyte in the original sample can be determined. Concentration can be calculated using a calibration curve created by finding the response for a series of concentrations of analyte, or by determining the response factor of an analyte. The response factor is the expected ratio of an analyte to an internal standard and is calculated by finding the response of a known amount of analyte and a constant amount of internal standard (a chemical added to the sample at a constant concentration, with a distinct retention time to the analyte).