questions on logistics modeling

While studying logistic modeling, I read the following statement

The fact that only odds ratios, not individual risks, can be estimated from logistic modeling in case-control or cross-sectional studies is not surprising.
I do not know what do the "case-control" and "cross-sectional studies" stand for in the statistical analysis? Moreover, I do not quite understand what does the above statement mean from the viewpoint of statistical analysis. Any explanations will be appreciated.