To ensure one's safety or success by dealing with every potentially problematic aspect of a situation or activity. A reference to baseball, in which the defensive players must make sure all bases (and baserunners who may occupy them) are accounted for. Primarily heard in US, South Africa. We have to be sure to cover our bases before the trial begins so that we aren't surprised by anything the prosecution throws our way.

To be well-prepared for every possible outcome. We need to cover all bases here—check every office and make sure it's been evacuated. I know I don't have the best grades, so I covered all bases by applying to 15 colleges.

To found or root something on a particular idea or occurrence. A noun or pronoun can be used between "base" and "on" or "upon." My love of science is based upon an interest in experimentation. Unfortunately, she has a low opinion of me. I think she based it on our first meeting, which didn't go well.

To account for or provide a way to address every possible outcome, scenario, contingency, etc. We need to cover all the bases here—the investigation should explore every avenue. I covered all the bases by applying to 15 colleges.

To include, make reference to, or take action on every desired or required element or aspect (of something). The essay touches all bases, but it doesn't do much to elaborate on them or introduce any new insights. For fans of the genre, the film touches on all the bases.

In baseball or softball, for a baserunner already on base to advance to the next base before or during a pitch (as opposed to when the ball is hit into play). The base is often specified (e.g. "steal second base"). After the wild pitch, the player on second managed to steal third base. He holds a record for stealing bases, typically managing to do it once or twice per game.