Correlation is the interrelationship between two or more variables. It is decisive for the dependence of one variable on another. If a direct relationship of one variable to another can be determined, then the correlation is high, in the other case, if no interrelationships exist, the correlation is low. The measure of correlation is expressed in the correlation coefficient.
Direct correlations exist, for example, in electronics in thermistors between the temperature and the resistance value of the thermistor, or in photoresistors between the incident light and the resistance value.
If there is a linear relationship between the relationships, it is a linear correlation; if it is nonlinear, it is a nonlinear correlation. If there is a similar relationship between the relationships, for example, if the resistance value increases with increasing temperature, then it is a positive correlation, which is reflected in a positive correlation factor, if the relationship is opposite - for example, if the resistance value decreases with increasing temperature - then the correlation is negative.
Correlation techniques are used in programming, compression techniques, and statistics, among others.
If a correlation occurs between two variables at different times, it is called an autocorrelation or cross-correlation.