My mother was just told that we found a density in her lungs from a ct scan? what does that mean?

Different things...: It could be related to different problems: a completely benign lesion, tumor, infection, inflammatory nodule( for multiple reasons), lymph nodes which most of the time are benign. If significantly large it might need biopsy but that requires a Pneumologist(Lung doctor) opinion and evaluation in order to decide the next step and inform more about diagnosis.