Governance is the act or process of governing or overseeing the realization of (the results associated with) a set of objectives that are owned by a single party, in order to ensure these results will be fit for the purposes that this party intends to use them for. This act or process is conducted by (agents that do so on behalf of) this party.
Governance is about planning the budgets and other resources necessary to (obtain and to) actually use the results. This includes the specification of timelines (deadlines) for the results to become available, as well as the properties and other characteristics (security, quality, sustainability, etc.) that results must have in order to make them effective ('fit for purpose' - fit to be used as intended by the consuming party). In order to keep tabs on the fitness of the results for the intended purposes, effectiveness indicators may be developed, i.e. gauges that measure how 'fit' the results are to be used/consumed for the intended purposes, are also part of this governance.
The purpose for a party of having a governance process is that it enables him to oversee the realization of (the results associated with) various subset of its objectives, and to change the specification of the associated results, to select the appropriate party for actually realizing these results, etc.