SPSS is a software used for Statistical analysis. It stands for Statistical Packages for Social Sciences. SPSS can perform almost any Statistical analysis, be it testing, ANOVA, regression or simply the graphical representation of the data. It is a very simple software to use and a person from non-statistical background can use it with ease. It only requires entering data and performing the necessary steps from it's easy to use menu. No technical coding or deep understanding is required. That is why it is one of the most widely used software by people of almost all fields.
SPSS restricts analysis of very large data sets. Also since it only takes the data and generates output the procedure employed to reach the results is not revealed as compared to some other Statistical analysis tools. That is why some people from core statistical background do not encourage using it.