Misuse of data analysis to find patterns that can be presented as statistically significant. Done by performing many statistical tests and only reporting those that have yielded significant results.
Data dredging (also data fishing, data snooping, data butchery, and p-hacking) is the misuse of data analysis to find patterns in data that can be presented as statistically significant, thus dramatically increasing and understating the risk of false positives. This is done by performing many statistical tests on the data and only reporting those that come back with significant results.
Source: Smith & Ebrahim "Data dredging, bias, or confounding: They can all get you into the BMJ and the Friday papers" (2002) via Wikipedia.
