In general, insufficient evidence refers to when an attorney does not meet the burden of proof in the case that they are arguing.
All cases have a set standard of proof, depending on the matter that is at issue. If that standard is not met, the court can dismiss the case due to insufficient evidence.
The different standards of proof are as follows, from the lowest to the highest standard: reasonable suspicion, reasonable to believe, probable cause, some credible evidence, substantial evidence, preponderance of the evidence, clear and convincing evidence, and beyond a reasonable doubt.