In its minimalist sense, wisdom is simply the ability and inclination to make choices that stand the sense of time. To say that a choice was wise implies that the action or inaction was strategically correct when judged by some set of values. In this sense, if a decision was, in retrospect, very smart, it was wise.
Another formulation along these lines is that wisdom is "Making the best use of available knowledge."
However, in a deeper sense, wisdom connotes an enlightened perspective and/or effective support for the long-term common good.
Insights and acts that are widely considered wise tend to
• arise from a broad (not narrow-minded) perspective,
• serve life in some broad or deep way (not just narrow self-interest)
• be grounded in but not limited by the past (experience, history, etc.) and the future (likely consequences)
As with all decisions, a wise decision is made from incomplete information. But in a wise decision the chooser possesses a sense of the way that situations usually turn out and, in its deeper forms, a desire for the outcome to be broadly beneficial.
Classically, wisdom is considered to come with age. In some religions, wisdom is considered a gift granted by God.
A wise person is often called a "sage."